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string | link
string | tags
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401
|
dsp
|
a moving average relation that I can't find a counter-example to
|
Hi: I'm new to this list but I had a question that's not exactly related to dsp but maybe in a slight way and I didn't know where else to send it. So, here goes and my apologies if this is totally the wrong place to send it.
The following describes the background as far as number generation.
Suppose have a series of positive numbers coming in sequentially ( regularly spaced ) that are generated by some invisible machine or oracle. no distribution is assumed for these numbers ( except that they are positive ) and they are generated at t1, ... tn. they are labelled as $x_1, x_2, ... x_n, x_{n+1}$. at each time $t$, the moving average with window size $n$ of the log of the $x_i$ is calculated and is labelled $mavelogx_t$.
the parameters of are $n$ and $d$. $n$ is the length of the moving average calculated at each time $t$. $d$ is positive and will be explained below.
The following describes the game for a player who decides to play given the above ( assuming that atleast n numbers have been generated by now so a moving average can be calculated ). It doesn't cost anything to play this game.
The player of the game sees a new number at time $tstar$, $x_{tstar}$, and if $log(x_{tstar})$ is $d$ less than the current moving average, $mavelogx_{tstar}$, then $x_{tstar}$ is marked as the player's "initial" number. like 36.83 or whatever. the game works so the next time $log(x_t)$ crosses the moving average, $mavelogx_{t}$, from below at say $t = tstarstar$, then $x_{tstarstar}$ is marked as the player's ending number and the game ends.
The game rule is such that at $t = tstarstar$, the game ends and the player receives $winnum$ = $log(tstarstar) - log(tstar)$ ( winnum could be negative in which the player of course pays ). Of course it could happen that the player never get an initial number or that the player gets an initial number and never gets an ending number but let's make the assumption that the player plays and the game both starts and ends.
Now, I claim ( and think I proved ) the following two things. ( really one because it's an if and only if ) are true for the player playing the game.
A) if $(tstarstar - tstar)$ turns out to be less than $n$, then $winnum$ has to be positive. similarly if $(tstarstar - tstar)$ turns out to be greater than or equal to $n$, then $winnum$ has to be non-positive.
and conversely
B) if $winnum$ is positive, then $(tstarstar - tstar)$ has to be less than $n$. similarly, if $winnum$ is not positive , then $(tstarstar - tstar)$ has to be greater than or equal to $n$.
I could send the proof to anyone who is interested but my questions were :
A) does anyone have a counter-example to disprove what I'm saying in A) or B).
B) if A) and B) are true ( my proof is correct ), then is this a well known result in the literature ( any literature. doesn't have to be DSP ) ?
thanks a lot. Mark
|
https://dsp.stackexchange.com/questions/9915/a-moving-average-relation-that-i-cant-find-a-counter-example-to
|
[
"algorithms"
] | 5 | 2013-07-12T06:20:42 |
[
"also, a different explanation of the same problem is in the article at arxiv.org/abs/1212.4890. it's very long but might be clearer. thanks again.",
"sorry jason. my mistake. it should read that $winnum = log(x_{tstarstar})−log(x_{tstar})$. thank you for pointing that out.",
"The above description of your game is very difficult to understand. I would try to clarify it with a more succinct explanation. For instance, I don't see how $t^{**}$ could ever be less than $t^*$ according to your description, so $log(t^{**}) - log(t^*)$ would always be nonnegative."
] | 3 |
Technology
| 0 |
402
|
mattermodeling
|
Contribution in action from collisions for a gas?
|
So if I write the [action](https://en.wikipedia.org/wiki/Action_\(physics\)) for a gas:
$$ S = \int (T -U) dt \tag{1}$$ where $T$ is the kinetic energy and $U$ is potential energy.
I suspect there is a constant term (which does not affect the equations of motion) for the gas (in classical mechanics). I was hoping to verify my ~~[paper's](https://drive.google.com/file/d/1deuIYhorbMBnIRoblhe_0q1P4CkIx3DD/view?usp=sharing) idea ~~ (There is now an updated version see [here](https://drive.google.com/file/d/1K95v8crlBWsf2_3kFiEbRDMNa5xVBdOV/view?usp=sharing)) up to equation $(19)$.The summary of ideas section wise are as follows:
$(1.1)$ We consider an arbitrary potential which $0$ everywhere until both the gas molecules collide.
$(1.2)$ Assuming a non-ideal collision (finite collision time) I get a non-zero action
$(1.3)$ We use Newton's second law to find the finite collision time and the average force is considered as pressure.
$(1.4)$ The deformed face of the molecule has an area which is also considered.
$(1.5)$ Since we are considering $2$ spheres colliding which is a function of their relative velocity we can find the average momentum change assuming the collision is not a special event.
$(1.6)$ The collision per unit 4-volume is mentioned as derived by Einstein.
Combining all the above subsections we derive a constant action term:
$$S_c = \int \frac{N R \tilde V'(2R)}{\pi} \frac{ \langle \mu \rangle \lambda }{k_B } dt \tag{2}$$
where $N$ is the number of particles, $R$ is the radius of the particle, $ \tilde V'(x)$ is the spatial derivative potential and $ \frac{ \langle \mu \rangle \lambda }{k_B } $ are constants.
Is this expression correct?
|
https://mattermodeling.stackexchange.com/questions/8498/contribution-in-action-from-collisions-for-a-gas
|
[
"molecular-dynamics",
"thermodynamics"
] | 8 | 2022-01-07T07:08:23 |
[
"(by linking to your paper you are now Less Anonymous :)"
] | 1 |
Science
| 0 |
403
|
puzzling
|
REALLY important days in history
|
@Z. Dailey asks a mathematical puzzle [Important days in history... and to come!](https://puzzling.stackexchange.com/questions/29503/important-days-in-history-and-to-come) with a series of dates in years 1973, 1978, 1983, 1992, 2005.
My puzzle asks the question: What is the previous date in my series? Explain!!
.......... .., .....
June 22, 1973
.......... .., .....
June 16, 1978
June 11, 1983
March 25, 1992
April 14, 2005
Hint:
> "rudder as a male swan"
|
https://puzzling.stackexchange.com/questions/29533/really-important-days-in-history
|
[
"knowledge",
"pattern",
"number-sequence",
"sequence",
"history"
] | 22 | 2016-03-24T02:41:27 |
[
"I'm assuming it's not January 3, 1972 and April 1, 1975...",
"@Haobin Is the hint in any way related to the Lufthansa logo?",
"Nothing failed about it. Also it's valid from a math p.o.v. ;check the MM/DD also.",
"@Overmind I would question your failed conclusion.",
"Logic dictates there's a high chance that the year is 1969, the fake moon landing year.",
"Apparently ebhtu nf n pbo is a phrase",
"A male swan being a rot13(pbo)"
] | 7 |
Culture & Recreation
| 1 |
404
|
puzzling
|
Can you find the cipher that I used?
|
I have encoded a phrase, using a cipher that I invented. But I don't want you to decode it, rather I want you to figure out how my cipher works.
This is the phrase that I encrypted
> Find the connection between this phrase and the output. You don't even have to do any solving, just figure out how this was encrypted
This is the key that I used
> A Blemished Orange
This is the encrypted phrase
> 1YaF7\B*,IdM#mI7\$iEB8lbnOKl5o.f9,J+772V2??16;XV2[)nhOov4elOT@h?Iw7nAO-2Nt2*,Sdq7XW&lBW0%^>u-C>,0)XSV&(627K,lHw7XeL8\B$PSj@[7n?PBbYbm@
These are important, but you'll have to figure out how
> 20
>
> 9100, 9129
>
> Python
That's everything, see what you can find!
|
https://puzzling.stackexchange.com/questions/96886/can-you-find-the-cipher-that-i-used
|
[
"cipher"
] | 11 | 2020-04-09T08:43:03 |
[
"That's much better, nice job! +1."
] | 1 |
Culture & Recreation
| 0 |
405
|
puzzling
|
A Glutton and a Split Check
|
**N** , **T** , **A** , **B** are arbitrary constants in this problem. I have only definitively solved the **N=1** subproblem, so, if the general problem cannot be solved, I will be satisfied to mark as accepted a solution to this subproblem. I may put a bounty out for the general solution before that.
## Problem Statement
You and **N** friends are seated at a restaurant, where you have agreed to equally split the check for \$**T**. The dining process consists of a waiter going around the table, asking each guest in turn to order an entrée costing any amount of \$1, \$2, ..., up to \$**A** (you cannot skip an entrée). The meal is of course over once the \$**T** limit has been reached (it cannot be exceeded).
The vain glutton that you are, you want to:
1. eat more than you pay for (that is, \$**T/(N+1)**), but also;
2. not be exposed as a glutton, which in this case consists of eating more than \$**B** extra than the next most expensive eater. If (1) cannot be achieved, you will nonetheless consider it a victory to see someone _else_ exposed in such a fashion.
Assuming you are first to order, for what values of **N** , **T** , **A** , **B** can you guarantee victory, no matter how your friends order? Keep in mind, they may conspire to make it difficult for you...
## Example
If **(N, T, A, B) = (1, 21, 13, 10)** , your gluttony might tempt you to order the most expensive \$13 entrée right off the bat. This would be a mistake, because your friend could thereafter order only \$1 entrées and expose you as a glutton. Similarly, you shouldn't order an \$11 or \$12 entrée. Yet if you order a $10 entrée or less, your friend may order an \$11 entrée, and you wind up paying for more than you eat while he cannot be exposed. So, there is no victory in this example configuration.
|
https://puzzling.stackexchange.com/questions/111330/a-glutton-and-a-split-check
|
[
"mathematics",
"strategy",
"game-theory"
] | 9 | 2021-08-16T15:49:43 |
[
"@Feryll Ah sorry, missed that N was your friends, not the number of people at the table. I see now the problem statement clarifies that. Thanks!",
"You have N friends, so, there are N+1 people in total who have precommitted to splitting the $T check. What they have not decided in advance is who is ordering what.",
"Hmm I just re-read the question and I'm a bit confused. How are they \"equally splitting the check for \\$T\" if by the definition of the rest of the problem some people are ordering food that costs more than others' orders? Is everyone spending \\$T/N regardless of how much they ordered for? If so, then not sure I understand \\$T/(N+1) -- if everyone is spending \\$T/N then aren't you \"eating more than you pay for\" starting from orders worth \\$(T/N)+1 or more, rather than \\$T/(N+1)? Are the parentheses applied incorrectly in the problem statement?",
"@Petr Naryshkin He will go around the table as many times as it takes to reach a total check of T, yes.",
"If the waiter gets all your orders and the check amount T is not reached (like in your example) does he start another round? If not, do you want to still eat for at least T/(n+1) or only for (total check)/(n+1)?",
"Reminds me of this a little bit en.wikipedia.org/wiki/Pirate_game",
"Funny, N>1 case seems easier than N=1, because the other's don't have to worry about being exposed (unless b=0). Still, too many cases for me ;-)",
"Yes, it says so in the least paragraph of Problem Statement :)",
"Are you the first to order?"
] | 9 |
Culture & Recreation
| 0 |
406
|
puzzling
|
Who wins the game of "Sticky Gomoku" on an infinite board?
|
This is a [Gomoku](https://en.wikipedia.org/wiki/Gomoku) like game, played by two players with Go pieces (black and white stones) on an infinite (in all four directions) Go board.
Rules
1. **Four in a row:** players alternate turns placing a stone of their color on an empty intersection. Black plays first. The winner is the first player to form an unbroken chain of four stones horizontally, vertically, or diagonally.
2. **Sticky:** except for black's first stone, every stone must be placed adjacent to one of your opponent's.
Question: can black force a win?
|
https://puzzling.stackexchange.com/questions/112346/who-wins-the-game-of-sticky-gomoku-on-an-infinite-board
|
[
"game",
"board-games"
] | 7 | 2021-10-28T02:56:16 |
[
"@Eric I see, thanks for the clarification! I guess it would be very hard to solve, as one doesn't expect to find a finite game tree that totally describes optimal moves.",
"@WhatsUp I heard of this game from an internet friend, who allegedly had invented it a few years ago, and had played it with friends since. The conjecture is that optimal play for both players will end in a draw, but no one is sure.",
"Looks like a funny game to play with family or friends, but I suspect that a systematic study would simply be an exhaustive search, probably computer-aided. Maybe @Eric can clarify whether there is a clever approach to be expected.",
"The only possible endgame I think is to create two 3-in-a-rows with one move, where the move itself and the two fourths are pairwise adjacent (forming a small triangle). Obviously the problem is how to force such a position in the first place...",
"This is actually much tricker than I thought. Getting 3-in-a-row is rarely an immediate threat because the blank space is usually not adjacent to the opponent and so not immediately playable.",
"@BenjaminWang Sure. Every intersection has eight adjacent neighbors.",
"Does \"adjacent\" include diagonally adjacent?"
] | 7 |
Culture & Recreation
| 0 |
407
|
puzzling
|
Best moves for a 7X7 4 queen board
|
There is a 7x7 board and 2 players, each having 2 queens. The queens can move just like the queens in chess, but cannot capture each other. At the beginning, the first player places both the queens on any 2 different squares. Then the second player does the same with his queens. From this point, the players alternate turns, moving both queens each turn. When a queen is moved, the square that was previously occupied is now blocked and cannot be stood on or moved across for the remainder of the game. The first player who is unable to move any of his queens loses!
I am designing a player for it. What will be the strategy for the player who starts first or second? Also, what are best starting moves for any player?
|
https://puzzling.stackexchange.com/questions/59804/best-moves-for-a-7x7-4-queen-board
|
[
"board-games"
] | 7 | 2018-01-25T21:09:16 |
[
"@SuhailGupta I hope that this answers most of your doubts. [1]:",
"didn't read the \"can't move across\" part sry, so I guess they can't.",
"@Untitpoi How does it matter?",
"If I have two queen in A1 and B1 can I make the queen in A1 move into C1? At the same time I choose to move my queen in B1 in C3! In other word are the moves of the two queen (of the same color) simultaneous or sequential.",
"I made a suggested edit to clarify the rules. If I got anything wrong please edit or roll back.",
"@Bass No. As the question says the end will be: \"The first player who is unable to move any of his queens loses!\"",
"Since \"the queens can move just like the queens in chess\", can they also capture the opposing queens?",
"@elias Both of his queens",
"It's still unclear for me if a player should move both his queens on his turn, or only one of them. Please clarify!",
"@prog_SAHIL The first move could be (3,4) and (5,5) for player 1 and then move for player 2 could be (1,2) and (2,2)",
"Can you please give an example for first 3,4 moves. Its hard to understand the rules.",
"After the first player has placed his two queens. They alternate their turns",
"When will the second player place the queens?"
] | 13 |
Culture & Recreation
| 0 |
408
|
puzzling
|
What is a 255b Word™?
|
This is in the spirit of the [What is a Word/Phrase™](https://puzzling.stackexchange.com/search?q=%22what+is+a%22+word+is%3Aquestion) series started by [JLee](https://puzzling.stackexchange.com/users/463) with a special brand of [Phrase™](https://puzzling.stackexchange.com/search?q=%22Phrase%22%20user%3A463%20is%3Aquestion) and [Word™](https://puzzling.stackexchange.com/search?q=%22What+is+%22+%22Word%22+-missing+user%3A463+is%3Aquestion) puzzles.
* * *
If a word conforms to a special rule, I call it a **255b Word™**.
Use the following examples below to find the rule.
$$ % set Title text. (spaces around the text ARE important; do not remove.) % increase Pad value only if your entries are longer than the title bar. % \def\Pad{\P{2.5}} \def\Title{\textbf{ 255b }} % \def\S#1#2{\Space{#1}{20px}{#2px}}\def\P#1{\V{#1em}}\def\V#1{\S{#1}{9}} \def\T{\Title\textbf{Words}^{\;\\!™}\Pad}\def\NT{\Pad\textbf{Not}\T\ }\displaystyle \smash{\lower{29px}\bbox[grey]{\phantom{\rlap{rubio.2019.05.15}\S{6px}{0} \begin{array}{cc}\Pad\T&\NT\\\\\end{array}}}}\atop\def\V#1{\S{#1}{5}} \begin{array}{|c|c|}\hline\Pad\T&\NT\\\\\hline % \text{ AMBIGUOUSLY }&\text{ AMBITIOUSLY }\\\ \hline \text{ BOXING }&\text{ BOXER }\\\ \hline \text{ COMPLICATE }&\text{ COMPLEX }\\\ \hline \text{ DECENTRALIZE }&\text{ DECENTRALIZATION }\\\ \hline \text{ ENTERTAINMENT }&\text{ EXCITEMENT }\\\ \hline \text{ FINALLY }&\text{ FINISHED }\\\ \hline \text{ GEOGRAPHY }&\text{ GEOLOGY }\\\ \hline \text{ HENRY }&\text{ HIGUAIN }\\\ \hline \text{ INDICATION }&\text{ INCLINATION }\\\ \hline \text{ JUXTAPOSING }&\text{ JUXTAPOSITION }\\\ \hline \text{ KNOWLEDGE }&\text{ KNOWLEDGEABLE }\\\ \hline \text{ LIGHTNING }&\text{ LIGHTENING }\\\ \hline \end{array}$$
And, if you want to analyze, here is a CSV version:
255b Words™,Not 255b Words™
AMBIGUOUSLY,AMBITIOUSLY
BOXING,BOXER
COMPLICATE,COMPlEX
DECENTRALIZE,DECENTHALIZATION
ENTERTAINMENT,EXCITEMENT
FINALLY,FINISHEO
GEOGRAPHY,GEOLORY
HENRY,HIGUAIN
INDICATION,INCLINATION
JUXTAPOSING,JUXTAPOSITION
KNOWLEDGE,KNOWLEDgEABLE
LIGHTNING,LIGHTENING
The puzzle satisfies the series' inbuilt assumption, that each word can be tested for whether it is a 255b Word™ without relying on the other words. These are not the only examples of 255b Words™; many more exist.
**Problem: What is a 255b Word™? And why is the property called 255b?**
* * *
**Hint:**
> This rule is actually quite arbitrary. I don't think you can read my mind without the [steganography](/questions/tagged/steganography "show questions tagged 'steganography'") tag.
|
https://puzzling.stackexchange.com/questions/92184/what-is-a-255b-word
|
[
"steganography",
"computer-puzzle",
"word-property"
] | 7 | 2019-12-22T04:56:24 |
[
"@Jasen Yes, both are correct.",
"are both lists correct?",
"@Vepir Yeah, I deliberately misspelled a few letters in CSV. :)",
"Is the CSV misspelled? (\"DECENT'H'ALIZATION\" with 'H' in CSV, but with 'R' in the table) Is CSV purposely not fully capitalized? (such as 'g' in \"KNOWLED'g'EABLE\" and 'l' in \"COMP'l'EX\")"
] | 4 |
Culture & Recreation
| 0 |
409
|
puzzling
|
Need help with a cipher: "poems" with capital letters
|
I am trying to figure out a cipher I _think_ I found in a book from 1982 and it's a 36 year old mystery we are trying to solve (I will reveal the book if this turns out to be something so everyone can play along!). The book has several poems in it that has has lines that start with capital letters. There is also several things that should be capitalized (like a name or place) that aren't capitalized and things that randomly made their own line in the puzzle. I thought it was weird so I typed them out and there were double and triple letters. I tried putting them in online puzzle solvers but nothing came up except gibberish. I also thought maybe the spaces meant new words, but nothing!
There is another post that I saw (that's how I found this site) that was similar using a columnar transposition cipher but I'm not sure if it is the same!
Three of the twelve did not have any double letters and there are several others poems in the book that mean something.
> FCFTTNTNISSPISTWOFIDLTA
> AFIFOAFHWTGFTN
> ITNXTIAINWWFYFAAETLI
> BAIBFBOSFSPAFTSF
> LTYWTOWCABBOTWAFGT
> OMCSBSHHFOMEEOWBBBEWFW
> ATNHEJFSNRIIOTGGTT
> VMAAFAFAFSSCAAPTBWSTPYOOAT
> TWNWBAAYSSSELOY
> IOFEIYCANSITOHVTOFOLAIOTB
> PIDRTTDWWAIJAATUWOLATBDY
> WMBACRLBIFFTTIFCFSOBH
These are the "extra" poems:
> TNAESFSSFWBDFAEM
> WFFEFEGQBCCETHISTFFRDAIGTOLGAATRTPIATRASADBTNHAFCPCEGVEWTFF
> KTTT
> NWEGCTFFMTDSTFANATSSNH
> TTSIBMHAFFWTWOAAFETFF
> ASYFCTTWWFFFG
|
https://puzzling.stackexchange.com/questions/53173/need-help-with-a-cipher-poems-with-capital-letters
|
[
"cipher",
"real",
"unsolved-mysteries"
] | 6 | 2017-07-05T14:13:38 |
[
"thesecret.pbworks.com/w/page/22148585/To%20Do",
"@Rubio As far as I can tell no one has come up with this cipher. I believe the only ones that are important are the first letters (besides using the clues in the verse to guide you too) as part of a secret cipher for several reasons.Preiss doesn't give us a way in the book to match up the picture and the verse, only tells us to match them up.There are a ton of combinations that they could be so there has to be a way for us to tell which is which.If you google the verses you will see that things like oz and wonderstone aren't capitalize, but they should be because they are places/people.",
"Yes, its real and not gibberish. I will just tell you guys what the book is because I know I can't figure it out. Hopefully someone can and find one of the treasures. In 1982 a guy named Byron Preiss wrote a book called The Secret, a Treasure Hunt and hid 12 casques throughout 12 North American cities. Since 19821, only 2 of the 12 have ever been found (Chicago in 1983 and Cleveland in 2004). The poems are long (all of them put together), otherwise I would post them. If you google the book you can find all the poems and what cities people think they are in. Good luck!",
"If this isn't real, forgive my edit",
"Can you post the full poem as well? How can we be sure that this isn't just gibberish you pulled?",
"How sure are you that the first letters are the only important parts here?"
] | 6 |
Culture & Recreation
| 0 |
410
|
puzzling
|
Rare but Abundant in Hill and Hole
|
> I am uncommon,
> But a worthy goal.
> Rare but abundant
> In hill and hole.
> Who am I?
You may already know the answer, so the task is not to answer the riddle per se, but to solve the following 'What is a Word' puzzle, use the words in the puzzle to find another four word phrase (2 from each side), and explain how the phrase provides/validates the answer to the above riddle.
> What is an Uncommon Word?
>
> If a word conforms to a special rule, I call it an Uncommon Word.
> Use the examples below to find the rule.
Uncommon Words | Not Uncommon Words
---|---
FEW | LOTS
MANY | ALL
RARE | ATYPICAL
TIE | UNHINGE
IA | RI
BAGGED | TOSSED
DOOMED | PERISHED
GAPING | BEHOLDING
ADO (2x) | TWICE
SEAL | REFUSE
HAVE | LACKED
ROUNDS | TURNS
SPITS | SPITES
> These are not the only examples of Uncommon Words, many more exist.
Hint:
> Teepee is an extremely common word.
> Quitting is an extremely uncommon word.
> Puddle is a quite uncommon word and also quite relevant. What property makes something uncommon?
Hint 2:
> I updated a word so that all the uncommon words are in an American scrabble dictionary rather than simply being American-English words, to help solvers identify them. Also added a very useful tag.
|
https://puzzling.stackexchange.com/questions/109321/rare-but-abundant-in-hill-and-hole
|
[
"riddle",
"word",
"pattern",
"word-property",
"letters"
] | 6 | 2021-04-07T21:21:04 |
[] | 0 |
Culture & Recreation
| 0 |
411
|
cs
|
Can a calculus have incremental copying and closed scopes?
|
A few days ago, I proposed the [Abstract Calculus](https://medium.com/@maiavictor/the-abstract-calculus-fe8c46bcf39c), a minimal untyped language that is very similar to the Lambda Calculus, except for the main difference that substitutions are `O(1)` (i.e., variables only occur once) and copying is an explicit, constant-time and incremental operation. Here is an example:
let (a & b) = (λx. λy. λz. y) in (a & b)
---------------------------------------- step 0
let (a & b) = (λy. λz. y) in (λx0. a) & (λx1. b)
------------------------------------------------ step 1
let (a & b) = (λz. y0 & y1) in (λx0. λy0. a) & (λx1. λy1. b)
------------------------------------------------------------ step 2
let (a & b) = y0 & y1 in (λx0. λy0. λz0. a) & (λx1. λy1. λz1. b)
---------------------------------------------------------------- step 3
(λx0. λy0. λz0. y0) & (λx1. λy1. λz1. y1)
Here, the `let (a & b) = t in k` syntax substitutes the occurrences of `a` and `b` in `k` by `t`, except it does so incrementally: notice how each lambda is pulled one by one.
There is a problem, though. Eventually, you'll try to pull a lambda which has a variable that is bound in `t`. That's occurs with `y` behind step 1. To solve that issue, whenever that happens, the bound variable `y` is replaced by `y0 & y1`, which are bound to each of the two copied lambdas, respectively. The problem with that is this requires us to abandon the notion of scopes, as, now, the bound variable of a λ can occur outside its own body (such as `y0` and `y1` behind step 2)!
Despite sounding bizarre, the language operates very well. You can represent the usual λ-encodings on it, implement recursive algorithms and it is compatible with the oracle-free fragment of the optimal reduction algorithm. Yet, some have questioned the absence of scopes. I've spent some time reasoning about this and couldn't find a way to have both things. In fact, it looks impossible. As a sanity check, I'd like to know if my reasoning makes sense.
**Thus, my question is: is that possible? Can we have both incremental copying and closed scopes in a calculus?**
|
https://cs.stackexchange.com/questions/96798/can-a-calculus-have-incremental-copying-and-closed-scopes
|
[
"lambda-calculus",
"type-theory",
"functional-programming",
"language-design"
] | 24 | 2018-08-27T17:09:19 |
[
"@chi I was reading Lamping's original paper right now, seems like he doesn't propose a textual calculus indeed. What I proposed is just a textual interpretation of his algorithm (in any of its stages). That representation can itself can be considered a calculus with 4 reduction rules, but requires abandoning the notion of scopes, which is what is puzzling me. Thanks (:",
"I'm not terribly familiar with graph-reduction techniques for the lambda calculi. I only remember that some later variants were much simpler than Lamping's (fewer brackets/special tokens around). Perhaps there's some way to represent those \"bracket\" rules in a term form? I vaguely recall a presentation stating that those rules could not be used on terms -- they really need graphs --, but I am unsure.",
"@augustss you're right, I should've clarified that I meant a language with abstractions λx. f.",
"@chi yes the reason I came up with this was to have an untyped (textual) language for Lamping's abstract algorithm. This is just a textual interpretation of that algorithm. Or do you mean he actually proposed such representation? I'm not aware of that, but would be very glad if that was the case. I'll check the paper again.",
"To me, this looks similar to the graph-reduction algorithms for (optimal) reduction in lambda calculus. The first paper IIRC was at POPL'90 by Lamping. There, the strict notion of scope is \"broken\" as it happens above, and replaced with a plethora of (indexed) bracket-markers in the term graph, which is reduced using small steps as above, duplicating terms gradually. I'd recommend you have a look at it, and subsequent (simpler) graph-reduction techniques.",
"SKI combinators have incremental copying, are (almost) isomorphic to the lambda calculus."
] | 6 |
Science
| 0 |
412
|
cs
|
Is the two-color leapfrog problem in P?
|
My question is whether a specific decision problem is in P or not. It's straightforwardly in NP. The decision problem is a specific case of the general $k$-color leapfrog problem.
I can already show that when $k=1$, the problem is in P. And when $k$ is unlimited, the problem is NP-complete. I have not been able to find an algorithm for the $k=2$ case, but I suspect it is in P. I am wondering if we can prove that it is in P, or (what would surprise me) that it is in fact NP-complete.
This question springs from an interesting discussion in a question I [previously asked](https://cs.stackexchange.com/questions/127268/is-the-leapfrog-automata-problem-in-p) on this site.
> **The $k$-color leapfrog problem**. Fix $k$. In a $k$-color leapfrog problem, you are given some number of transparent urns containing colored balls. Each ball is one of $k$ possible colors. You are also supplied with an _agenda_ , which is an ordered list of colors, for example "red, red, red, blue, red, green, ...". The object of the game is to draw balls out of the urns, one at a time, following the sequence of colors specified in the agenda. You can easily see the contents of all urns at all times, and can draw any ball out at will. If you could draw the appropriate color from multiple urns, you may choose which one. The only constraint is that you may not draw from the same urn twice in a row. You win the game if you complete the agenda, otherwise you lose.
>
> The decision problem is whether, for a given arrangement of urns and a given agenda, the game is winnable.
**The 1-color leapfrog problem is in P**. If there is only one color of ball, you can decide it with the following algorithm: at each turn, draw the ball from the urn with the most balls in it (among urns you're allowed to draw from). If the game is winnable at all, this algorithm will win it. (Note that even when $k=1$, a game may still be unwinnable if there's too great a disparity in ball count. For example, the setup ["R", "RRR"] with the agenda "RRRR" is unwinnable.)
**The $\infty$-color leapfrog problem is NP-complete**. See my [previous question](https://cs.stackexchange.com/questions/127268/is-the-leapfrog-automata-problem-in-p) and the dazzling solution provided. You can perform a reduction from SAT using a game with two new urns and three new colors per clause.
**What about 2-color leapfrog?** This is my main question. I suspect the problem is in P, as with the 1-color case, but the 1-color algorithm doesn't seem to generalize — or at least I'm not sure.
**Bonus: What about $k$-color leapfrog?** An interesting higher level question is where exactly the problem becomes hard. Is is still in P when $k=3$, or does the leapfrog game have a phase transition like 2SAT to 3SAT? Is perhaps in P for all finite $k$? I've been struggling to find an efficient algorithm— I suspect there might be one, just based on how the problem becomes smaller and smaller as you remove balls.
* * *
**Edit** : _The naive extension does not work._ Note that the "leveling" strategy — generally ensuring that the urns have approximately the same number of balls of each color by removing from the urn that has the most— perfectly solves the $k=1$ case. I expect finding an extension of this strategy will solve the $k=2$ case, but note that one naive extension does not work:
For the scenario where the urns contain [AAB, ABB] and the agenda requires AABBBA, the naive strategy of taking from the legal urn with the most of the requested color does not work. It fails to find a solution despite the fact that this instance is actually solvable. (Similarly, the strategy of taking each color from the urn that has the least amount of the _other_ color also fails on this problem instance.)
* * *
**Update:** In the special case that the agenda has the form $A^m B^n$ $(m,n\geq 1)$, you can determine whether it's solvable in polynomial time by playing two single-color games in series. Briefly put, a single-color game is winnable if and only if the vase with the most balls has at most one more ball than the rest of the vases put together. Equivalently, it's winnable if and only if you can pair up each ball with a ball from another vase, with at most one left over. You can construct a winning sequence of moves given such a pairing: first draw the unpaired ball if any. Then iterate over each pair in an arbitrary order. Because the pairs come from different vases, at least one of them will be legal to draw next; draw it, then the other one. Proceed until you draw all the balls.
Because you can iterate over the pairs in an arbitrary order, you can generally always choose a drawing order such that the last ball comes from the vase of your choice. Or, reversing the drawing order*, that the first ball comes from the vase of your choice. Hence in the two-color scenario, when the agenda is $A^mB^n$, you can solve it as follows: Pick a vase $V_A$ with an $A$-colored ball and another vase $V_B$ with a $B$-colored ball (if you can't, then there's only one vase and it has multiple balls in it, so the game is unwinnable). If it's possible to win the $A^m$, choose the winning strategy to draw from $V_A$ in the last step. If it's possible to win the $B^n$ game, choose the winning strategy to draw from $V_B$ in the first step. This can all be done and checked in polynomial time, QED.
[*] Actually, reversing a path is not always possible: if the vase with the largest amount has exactly one more ball than the rest of them put together, then you _must_ draw from the largest vase first. The proof for how to solve $A^mB^n$ in this case will have to wait.
* * *
**Update** : By exchanging the notion of urns and colors, you can get the following equivalent formulation:
> _Reformulated leapfrog problem:_ Fix $k$. You are given $k$ urns full of different-colored balls, and an agenda which tells you which urn you must draw from at each step. Your goal is to empty all of the urns subject to the constraint that each ball must be a different color from the one before it.
Perhaps rephrasing this way can be useful. Also in this reformulation, I think the complexity is exposed by supposing you have two urns, where the second urn contains at most two balls.
|
https://cs.stackexchange.com/questions/127611/is-the-two-color-leapfrog-problem-in-p
|
[
"complexity-theory",
"turing-machines"
] | 18 | 2020-06-24T01:51:59 |
[
"A case is a set of additional constraints that we might choose to impose. E.g., \"Is there a solution in which urns 3 and 5 finish with at least 1 A-ball each, and urns 2 and 5 finish with at least 1 B-ball each?\" The idea being to come up with a set of at most polynomially many cases such that (a) any solution to the original problem belongs to at least 1 case in the set, and (b) each of these more constrained problem instances can be solved in poly time -- solving each case would then give a poly-time algorithm. But now I think (b) is harder to achieve than I thought.",
"@j_random_hacker If we restrict either the maximum number of urns or the number of balls per urn, the search problem becomes polynomial, but I'm not sure yet that it's polynomial without those restrictions. In the first case, a game state lists the number of balls of each color in each urn. In the second, the contents of each urn have a constant number of possibilities, so a game state counts how many urns of each content-type there are. In both cases, the number of game states is polynomial in the input.",
"Thanks. I'm wondering what counts as a \"case\" --- is it a game state (i.e. the contents of each urn at a single point in time) or a game path (i.e. a sequence of draws to make)? Naively, there are a lot of paths --- each game state will generally have multiple ways to arrive at it, and some might not be legally reachable.",
"The above is not quite right: Once there is only one A left in the agenda, if there is only one urn with A-balls in it and it is also one of the 2 urns with B-balls, then we cannot necessarily choose B-ball urns freely. Still I think this problem can be attacked with a case analysis: Either there is a solution where we never drop below 2 A-ball urns and 2 B-ball urns; or a solution in which some urn becomes the only A-ball urn \"first\"; or a solution in which some urn becomes the only B-ball urn \"first\"; or no solution. There are only $O(n^2)$ such cases to consider.",
"If there are not enough As and Bs in total to cover the letters in the agenda, then clearly the instance is unsolvable. Otherwise, the only way to get stuck is to get into a situation where two adjacent agenda letters can only come from the same urn. So if you can choose urns in sequence so that, while $\\ge 2$ A-balls remain in the agenda, you have at least 2 distinct urns $a_1, a_2$ containing 1 or more A-balls, and similarly urns $b_1, b_2$ for B-balls (note $\\{a_1, a_2\\} \\cap \\{b_1, b_2\\}$ is allowed to be nonempty), you will get a solution. However this can miss some solvable instances.",
"As a follow up, note that when the agenda is a simple band of colors, e.g. AAAAAA or AAAAABBBBB, the problem is quite simple because it factors mostly like the $k=1$ case; the hard part is deciding what to do at the junctions between neighboring colors. If we can find a simple algorithm for the junctions, we can handle each color more or less separately and stitch them together in the end.",
"Assuming there is a polynomial algorithm, perhaps there's one that runs in time $O(n^k)$, where $k$ is the number of colors and $n$ is the problem size. This suggests an approach to designing an algorithm---iterate over each color, or even each pair of colors. And it would suggest why the problem becomes harder when the number of colors is unbounded so $k \\approx n$.",
"It seems I wasn't careful enough, so there's no issue with encoding (we can assume that each vase has at most the agenda's length balls of each color, and since the agenda is ordered this means we are allowed a polynomial number of operations in the numerical value of the number of balls in each vase).",
"@Ariel Can you, please, elaborate on the $O(n^3)$ algorithm from your previous comment? If I understand you right, you will have to fill a $(n + 1)$-dimensional table with $n$ elements in each dimension at the worst case. But it will give an $\\Omega(n^{n+1})$ time complexity.",
"My mistake, I missed the \"draw any ball at will\". The encoding becomes important here, each vase should be described as a histogram (n-white, m-black) otherwise the previous solution is polynomial.",
"@Ariel I should clarify that there's no order to the balls in each vase---you can see all of them, and pick any one out at will. The agenda is a separate structure, listing the sequence of colors you must draw (and you can pick which vases). I like your approach, though, and a similar algorithm definitely works for $k=1$ colors. Maybe we can make it work for $k=2$?",
"Have you tried dynamic programming? Given $n$ vases each described as a list of colors, our ability to win the game depends on $n+1$ parameters, the index of the active vase (constraint) and $n$ indices of locations in each list which indicate the number of balls we have drawn from each vase. If I'm not missing anything basic, this seems to admit to a straightforward $O(n^3)$ time algorithm (assume for simplicitly that $n$ is a bound on both the number of vases and the number of balls in each vase). It also seems to work for the $\\infty$-color problem, so I might be completely off.",
"@Juho Thanks for the tip! I'll look into color graph path problems; the leapfrog problem is definitely a special case of that. I suspect it's an easier special case, but if I can perform a reduction from GRAPH MOTIF, that'll establish that it's in fact just as difficult.",
"It sounds similar to a problem in which you want to find a path in a (directed) graph with specified colors (in order). These type of problems are usually hard (like GRAPH MOTIF, which IIRC is hard for 2 colors even on trees). Your visitation constraint might complicate things a little (or maybe you can avoid it) but a reduction from such a problem might be short and simple."
] | 14 |
Science
| 0 |
413
|
cs
|
Test whether two languages are equal, when give in algebraic form
|
This sub-problem is motivated by [Algorithm to test whether a language is regular](https://cs.stackexchange.com/q/18010/755).
Suppose we have two languages $L_1,L_2$ that are expressed in "algebraic" form, as formalized below. I want to determine whether $L_1 = L_2$.
Is this decidable? If yes, can anyone suggest an algorithm for this? If not, can anyone suggest a semi-algorithm (one that returns "equal", "not equal", or "I'm not sure"; where we want it to return "not sure" as rarely as possible).
Motivation: A solution to this sub-problem would be helpful for solving [Algorithm to test whether a language is regular](https://cs.stackexchange.com/q/18010/755)
* * *
**Algebraic form.** Here's one possible definition of what I mean by a representation of a language in algebraic form. Such a language is given by
$$L = \\{E : S\\}$$
where $E$ is a word-expression and $S$ is a system of linear inequalities over the length-variables, with the following definitions:
* Each of $x,y,z,\dots$ is a word-expression. (These represent variables that can take on any word in $\Sigma^*$.)
* Each of $x^r,y^r,z^r,\dots$ is a word-expression. (Here $x^r$ represents the reverse of the string $x$.)
* Each of $a,b,c,\dots$ is a word-expression. (Implicitly, $\Sigma=\\{a,b,c,\dots\\}$, so $a,b,c,\dots$ represent a single symbol in the underlying alphabet.)
* Each of $a^\eta,b^\eta,c^\eta,\dots$ is a word-expression, if $\eta$ is a length-variable.
* The concatenation of word-expressions is a word-expression.
* Each of $m,n,p,q,\dots$ is a length-variable. (These represent variables that can take on any natural number.)
* Each of $|x|,|y|,|z|,\dots$ is a length-variable. (These represent the length of a corresponding word.)
My goal is something rich enough to capture many of the examples we see in textbook exercises. (Feel free to suggest modifications to this formalization if it makes the equality-testing problem easier while still remaining expressive enough to capture many of the examples we see in textbooks.)
* * *
**Some easier cases.** If the original problem is too hard, here are some sub-cases that would still be interesting:
* If $L_1,L_2$ are two languages specified in "algebraic" form as above, and $L_1\ne L_2$, let $d(L_1,L_2)$ denote the length of the shortest word that is an element of one of $L_1,L_2$ but not the other. Can we upper-bound $d(L_1,L_2)$ as a function of the length of the descriptions of $L_1,L_2$? Is it guaranteed to always be polynomial? at most singly-exponential?
Motivation: If we could prove it is always polynomial, this might help us exhibit a witness that $L_1 \ne L_2$.
* If we omit the reversal operation (we do not allow $x^r,y^r,\dots$), does the problem become easier?
|
https://cs.stackexchange.com/questions/18062/test-whether-two-languages-are-equal-when-give-in-algebraic-form
|
[
"algorithms",
"formal-languages",
"regular-languages",
"decision-problem"
] | 15 | 2013-11-15T19:08:21 |
[
"If it is limited to regular languages, then you can compare them. Regular languages can be converted to finite state machine. And if you minimise two different finite state machines and you end up with the same answer for both, then they are infact the same. (They both handle the same language if they simplify to the same form.) You won't be able to do this for a CFG language, otherwise you would have solved the halting problem.",
"I don't see how to express Dyck languages in this framework.",
"@FrançoisG., no. For instance, $\\{w^\\eta w^\\eta : w \\in \\Sigma^*, \\eta \\in \\mathbb{N}\\}$ is not context-free but has an algebraic form. (I don't know whether every context-free language has an algebraic form expression; I don't see any reason to expect this to be true.) I know that testing equality of two context-free languages is undecidable. I don't know how hard the first sub-case (at the end of the question) is if $L_1,L_2$ are two context-free languages.",
"Are those algebraic form languages and context free languages the same ?"
] | 4 |
Science
| 0 |
414
|
cs
|
What can be proven regarding the differences in power between unary ECMAScript regex functions and primitive recursive functions?
|
In 2014, inspired by [Regex Golf](https://alf.nu/RegexGolf), I started exploring, along with a mathematician going by the name **teukon** , what could be done in the unary domain in ECMAScript regex that went significantly beyond matching primes and powers of 2 (both of which were puzzles in the Regex Golf site). This is a dialect of regex that includes negative and atomic positive lookahead, and backreferences that are erased when the loop they were defined in starts a new iteration. (They're of course not "regular expressions" in the CS sense).
A unary regex function takes a string of identical characters as input (`x` is used for clarity instead of `1`), whose length represents $n \in \mathbb{N_0}$. Its output may be either a non-match (which can represent "false"), or any $m \le n$ (which can represent "true", ignoring $m$'s value).
Due to the limitations on ECMAScript backrefs, only one variable* can be changed from iteration to iteration in a loop – the the $tail$ following the current cursor position, in such a way that it is decreased by at least $1$ on every iteration (by moving the cursor forward). All other variables (backrefs) can only capture a value once (per iteration if in a loop) which cannot be greater than the value of $tail$ at the time of its definition. An additional constraint is that when searching for a number that satisfies some condition, the current value being tested must be subtracted from $tail$ before its properties can be tested (this can be avoided by defining a new operation, non-atomic lookahead, which allows the regex engine to backtrack into the lookahead from outside it). And $n$ can only be operated on directly when the cursor is at the leftmost position, i.e. $tail=n$.
Because of this, the approaches available in more powerful regex flavors (e.g. Perl, PCRE, Java, .NET, Python, Ruby) won't work, for example `^(^x|xx\1)*$` can't be used to match squares.
I was suprised and fascinated to find that the power of unary ECMAScript regex goes rather deep indeed:
* Match primes - [`^(?!(xx+)\1+$)xx`](https://codegolf.stackexchange.com/a/177196/17216)
* Match powers of 2 - `^(?!(x(xx)+|)\1*$)` or `^(?!(x*)(\1\1)+$)` or `^((x+)(?=\2$))*x$`
* Match powers of 10 - `^((x+)\2{8}(?=\2$))*x$`
* Match prime powers - [`^(?!(((x+)x+)(?=\2+$)\2*\3)\1+$)x`](https://codegolf.stackexchange.com/a/219939/17216)
* Match `N`th powers - [`^((?=(xx+?)\2+$)((?=\2+$)(?=(x+)(\4+$))\5){N})*x?$`](https://codegolf.stackexchange.com/a/21951/17216)
* Match correct statements of multiplication - [`^x(x*)·?(x*)·?x\1=(?=(x(\1\2))\1(\3*)\4*$)\3*$\5`](https://github.com/Davidebyzero/RegexGolf/blob/master/regex%20for%20matching%20multiplication%20-%20simple%20method.txt) (takes its input as `A·B=C`; doesn't handle zero); this uses the Chinese remainder theorem. Although it's not purely unary (with delimiters `·` and `=`), its multiplication logic can be used within a purely unary regex.
* Fully generalized, with handling of zero: [`^(?=(x?(x*))·(x?(x*))).*=(?=.*((?=\1*$)(?=\3*$)(?=\1\4+$)\3\2+$|$\1|$\3))\5$`](https://github.com/Davidebyzero/RegexGolf/blob/master/regex%20for%20matching%20multiplication%20-%20multiplication%20%2B%20comparison%20-%20fully%20generalized.txt)
* Division and remainder - [`(x(x*)),(x*?)(?=\1*$)(x?(x*))(?=\4*$)((?=\2+$)\2\5*$|$\4)`](https://codegolf.stackexchange.com/a/222932/17216)
* This turned out to be quite interesting. The algorithm can't be proved using the Chinese remainder theorem, but finally does have a proof (linked above) thanks to H.PWiz. There are shorter variants that can be used when certain inequalities regarding the dividend and divisor are guaranteed to be met.
* Match squares - [`^(x(x*)|)(?=(\1*)\2+$)\1*$\3`](https://codegolf.stackexchange.com/a/223201/17216) (shorter than the above Nth powers regex thanks to generalized multiplication)
* Match perfect powers ($a^b$ where $b>1$) - `^(x+)((\1(x+))(?=(\3*)\1*$)\3*(?=\4$\5))+x$|^x?$`
* Match triangular numbers - [`^((((x*)x?)\3)x)?(?=\4(\1*)\2*$)\1*$\5`](https://codegolf.stackexchange.com/a/220988/17216)
* Match Fibonacci numbers - [`^(?=(x*).*(?=x{4}(x{5}(\1{5}))(?=\2*$)\3+$)(|x{4})(?=xx(x*)\5)\4(x(x*))(?=(\6*)\7+$)(?=\6*$\8)\6*(?=x\1\7+$)(x*)(\9x?)|)(\9\10(\5\10)\12?|xx?x?|x{5}|x{8}|x{21})$`](https://codegolf.stackexchange.com/a/178956/17216)
* Match factorial numbers - [`^(((x+)\3+)(?=\3\3\2$)(x(?=\3+(x*))(?=\5+$)(?=((x+)(?=\5\7*$)x)\6*$)\3+(?=\5\7$))*\3xx|x?)x$`](https://codegolf.stackexchange.com/a/178979/17216)
* Match abundant numbers - [`^(?=((?=(xx+?)\2+$)(x+)\3*(?=\3$))+(?!\2+$)(?=(xx(x*?))\4*$)x((x(x*))(?=\7*$)\5\8+$))(?=(x(x*))(?=\9*$)\6\10+$)(?=(x*?)(?=(x(\6\7))+$)(x(x*))(?=\14*$)(?=\13+$)\15+(?=\11\11|(x))\13$)((?=(x*?(?=\9*$)(?=(x+)(?=\10+$)\19*$)(^\14{2}\16|)))(?=(xx+).*(?=\9$)(?=\21*(?!\19)\21$)(|(x+)\23*(?=\23$))(?!(xx+)(?!\21+$)\24+$)(?=(x*)(?=xx(x\25)*$)\21\25*$)(\21+$))(?=.*?(?!x\18)(?=(x(\27\25))+$)(x(x*))(?=\30*$)(?=\29+$)\29\31+$|)(?=\30(x*)(?=\9*$)(\21\10+$))\32)+\33$`](https://codegolf.stackexchange.com/a/178952/17216) (there is a shorter version, but I haven't proved it to be correct to infinity yet)
* Return $\lfloor{\log_2 n}\rfloor$ \- [`(?!(x*)(\1\1)+$)(?=(x+)\3)(?=((?=(x+)(?=\3)\5(((x*)(?=\8$)x)+$))\6)*)\5x|\b$`](https://chat.stackexchange.com/transcript/message/48931239#48931239)
* Return $\varphi(n)$ \- [`(?=((xx+)(?=\2+$)|x+)+)(?=((x*?)(?=\1*$)(?=(\4xx+?)(\5*(?!(xx+)\7+$)\5)?$)(?=((x*)(?=\5\9*$)x)(\8*)$)x*(?=(?=\5$)\1|\5\10)x)+)\10|x`](https://codegolf.stackexchange.com/a/180255/17216)
* Return $\lfloor{n\sqrt{1/2}}\rfloor$ \- [`(?=(x(x*)).*(?=\1*$)\2+$)(?=(x\1)+(x?(x*)))(?=\4(x(x*?))\1+$)(?=.*(?=(?=\4*$)\4\5+$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\9))(?=.*(?=(?=\4*$)(?=\6*$)(?=\4\7+$)\6\5+$|$\4)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\13))(?=.*(?=\12\12\9$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\17))(?*.*?(?=((?=\3*(x?(x*)))\21(x(x*?))\1+$)))(?=.*(?=\23*$)(\23\24+$))(?=.*(?=(?=\21*$)\21\22+$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\27))(?=.*(?=(?=\21*$)(?=\23*$)(?=\21\24+$)\23\22+$|$\21)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\31))(?=.*(?=\30\30\27$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\35))(?=.*(?=\26\26)(?=\3*(x*))(\1(x)|))(?=.*(?=\34\34\40)(?=\3*(x*))(\1(x)|))(?=(?=(.*)\13\13\17(?=\6*$)\6\7+$)\44(x+|(?=.*(?!\16)\41|(?!.*(?!\38)\8).*(?=\16$)\41$))(\25\31\31\35){2}\43$)\20|xx?\B|`](https://codegolf.stackexchange.com/a/198428/17216) \- uses `(?*`...`)`; without that, it'd be about twice as long or more. This can clearly be extended to any algebraic number $0<x<1$; $x=\sqrt{1/2}$ is probably the simplest irrational example.
*So in order to emulate more than one mutable variable in a loop, a tuple must be encoded into a single number. For example:
* The encoding $(a,b,j)\to a+b^2+jC$, where $j$ is a decreasing iteration count, works as long as $a\le 2b$ and $(b+1)^2\le C$ always remain true and $(j_0+1)C-1\le n$. The values of $a$ and $b$ may increase or decrease from iteration to iteration.
* With the encoding $(a,b,j)\to a+bC+jC^2$, where $a<C$ and $b<C$, the values of $a$ and $b$ may increase or decrease from iteration to iteration without any inequality being enforced between them.
* The encoding $(a,b)\to n-a-b^2$ works as long as $a\le 2b$ and $a+b^2\le{n\over 2}$ remain true and $a$ and/or $b$ increase on every iteration.
I have [written a regex engine](https://github.com/Davidebyzero/RegexMathEngine) to facilitate exploring mathematical regexes. It's much faster than traditional regex engines when operating on unary numbers, not only because it can represent them as integers rather than strings, but also thanks to optimizing for common operations done on unary numbers. I also implemented non-atomic lookahead / molecular lookahead `(?*`...`)`, which was later also adopted by the regex engine PCRE2.
In 2019 I began to post mathematical ECMAScript regexes on [CGCC](https://codegolf.stackexchange.com/users/17216/deadcode), which got [Grimmy](https://codegolf.stackexchange.com/users/6484/grimmy) and [H.PWiz](https://codegolf.stackexchange.com/users/71256/h-pwiz) interested in the subject. Some nice advancements came from this, including huge golf optimizations, and at least one additional function being implemented that I previously wasn't sure was possible, $\varphi(n)$, and a rigorous proof of the division algorithm. But my core questions remain unanswered.
### Please note that although there are five questions below, I will upvote and accept any good answer to even just one of them.
My questions are:
1. Can any transcendental number $0<x<1$ be "computed" by an ECMAScript regex in the same way as $\sqrt{1/2}$ is computed by the regex above, i.e. by returning $f(n)=\lfloor{nx}\rfloor$? Trivial examples like $1.101001000100001...^{-1}$ might be possible. What about $\pi^{-1}$ or $e^{-1}$, or numbers whose class is not known, such as $\gamma$ or $\delta$?
2. How precisely can the power of unary ECMAScript regex be characterized? Can any primitive recursive functions in $\mathbb{N_0}$ where $f(n)\le n$ be proven to be impossible? It's obviously somewhere below primitive recursive in power, as its limitations surely make implementing some primitive recursive functions impossible. For example, I'm pretty sure [$\pi(n)$](https://en.wikipedia.org/wiki/Prime-counting_function) is impossible. (Given infinite scratch space to work in, instead of just $n$, it would be exactly primitive recursive in power – just search for an enormous number encoding all the relations to be tested, and consume them one at a time.)
3. Are there any functions that can be implemented with molecular lookahead `(?*`...`)` but not without it? Grimmy came up with an interesting problem that comes close: Match $n$ iff there exist perfect powers $a\le n$ and $b\le n$ (using the definition of perfect powers above) such that $n-a = (n-b)^m$ where $m>1$. This gives the sequence $20, 28, 29, 35, 41, 52, 68, 72, 89, 90, 126, 130, 133, 174...$
* In ECMAScript+`(?*)` this is just [`^(?*(x(x*)x+))(?!(\1|x\2)(?!(x+)((\4(x+))(?=(\6*)\4*$)\6*(?=\7$\8))+x$|x$)).*(?=\1$)\2((\2(x+))(?=(\10*)\2*$)\10*(?=\11$\12))+x$`](https://kingbird.myphotos.cc/b751bb38f1a1b12e90f23541f8f6ec33/regex%20for%20perfect%20power%20differences%20puzzle,%20with%20molecular%20lookahead.txt).
* In ECMAScript it's still possible: [`^(?=(x*)\1(x*))((x+(x*))(x?))(?=\6*(x?)).*(?=\1$)(?=.*(?=\2\7)(xx)?((\7?)x*))(?=\9*(x?))(?!\10(\4|\5)\6(?!$\11|(\11(x*))(?:(?=(?=\13$\9|(?=(\13\13\9)+(x*))(?=.*(?=\15)\16(x*))\17\15*$)((x*)(x|(?=(x))))(?=\21((?=\18$)|(?=(\18\18\21))(?=\18\18\23*(x*))(?=.*(?=\23)\24(x*))(?=\25\23*$)))((?=.*(?=\21$)\11(x*)|(x))(?=(\27\28))\21\14\28((?=.*(?=\29$)\20$)\19$|(?=(\19\19\20)+(x*))(?=.*(?=\31)\29\32(x*))\33\31*$)))(?=.*(?=\21$)\11$)\26\14)+$)).*(?=\6\4$)(\6(\5))(?:(?=(?=\34$\7|(?=(\34\34\7)+(x*))(?=.*(?=\36)\37(x*))\38\36*$)((x*)(x|(?=(x))))(?=\42((?=\39$)|(?=(\39\39\42))(?=\39\39\44*(x*))(?=.*(?=\44)\45(x*))(?=\46\44*$)))((?=.*(?=\42$)\6(x*)|(x))(?=(\48\49))\42\35\49((?=.*(?=\50$)\41$)\40$|(?=(\40\40\41)+(x*))(?=.*(?=\52)\50\53(x*))\54\52*$)))(?=.*(?=\42$)\6$)\47\35)+$`](https://chat.stackexchange.com/transcript/message/49026359#49026359) \- this works by pair-encoding variables.
With a little modification, it seems it should be possible to design a function that is not possible without `(?*)`. But could it be proven to be impossible?
4. Are there any functions that can be implemented with right-to-left evaluated variable-length lookbehind `(?<=`...`)`, as in the ECMAScript 2018 standard, but not with `(?*`...`)`? In most ways lookbehind gives a superset of molecular lookahead's power. `^(?*A)B` can be transformed to `^A(?<=(?=B)^.*)`. When we're not at the $tail=n$ position, `(?*A)B` can become `(?<=(.*))A(?<=^\1(?=B).*)`. Lookbehind can directly do things that molecular lookahead cannot; most notably, `^`...`(?:`...`(?<=(?=A)^.*)`...`)*`...`$` uses it to do tests directly on $n$ from within a loop. Are there functions that require this functionality, and can't be implemented with just `(?*`...`)`?
5. Are there functions that can be implemented with `(?*`...`)` but not with `(?<=`...`)`? Although the latter may seem at first to offer a strict superset of the former's functionality, this may not be the case. `(?:(?*A)B)*` can only be transformed to `(?:(?<=(.*))A(?<=^\1(?=B(.*)).*).*(?=\2$))*` if `A` never advances the cursor by more than `B`.
|
https://cs.stackexchange.com/questions/137112/what-can-be-proven-regarding-the-differences-in-power-between-unary-ecmascript-r
|
[
"complexity-theory",
"computability",
"space-complexity",
"number-theory",
"primitive-recursion"
] | 14 | 2021-03-25T14:34:10 |
[
"@Nayuki That logic doesn't work. The equivalent of only a finite number of digits of the transcendental number need to be calculated. By your logic, it wouldn't even be possible in a Turing-complete language to take a natural number N as input and calculate the first N digits of pi as output, but that is possible. (You may be falsely equating transcendental numbers with uncomputable numbers.)",
"\"Can any transcendental number computed\": No, because transcendental numbers are uncountable whereas program code strings are countable."
] | 2 |
Science
| 0 |
415
|
cs
|
Choosing a subset of binary variables to maximize the sum of the highest $K$
|
Consider the following problem:
**Input:**
* integers $n > m > k$;
* $n$ numbers $0 \leq p_1, \ldots, p_n \leq 1$;
* $n$ numbers $r_1, \ldots, r_n$ where ($r_i \geq 0$).
Let $X_1,\dots,X_n$ be $n$ independent random variables with distribution $X_i \sim \text{Bernoulli}(p_i)$ and define $Y_i = r_iX_i$.
**Output:** a subset $S$ of $[n]$ of size $m$ that maximizes $r_S = \mathbb{E}[Z_S]$, where $Z_S$ is the random variable $Z_S = \max_{T \subseteq S, |T|=k} \sum_{i\in T} Y_i$.
In other words, we want to select $m$ $Y_i$s such that the expected value of the sum of the largest $k$ of them is maximized.
Can this problem be solved in polynomial time?
Or is it NP-hard?
Is there an efficient $\alpha$-approximation algorithm?
* * *
Example:
**Input:**
* $n=3, m=2, k=1$
* $p_1=1.00, p_2=0.10, p_3=0.01$
* $r_1=2, r_2=11, r_3=100$
**Output:** the correct output is $S = \\{1,3\\}$. Why?
* $r_{\\{1,3\\}} = 2.98$: if $X_3=1$, then $Z_S=100$ (since $T=\\{3\\}$ in this case), otherwise $Z_S=2$ (since $T=\\{1\\}$ in this case), and thus
$$r_{\\{1,3\\}} = \Pr[X_3=1] \times 100 + \Pr[X_3=0] \times 2 = 0.01 \times 100 + 0.99 \times 2 = 2.98.$$
* $r_{\\{1,2\\}} = 2.9$: if $X_2=1$, then $Z_S=11$, otherwise $Z_S=2$, and thus
$$r_{\\{1,2\\}} = 0.1 \times 11 + 0.9 \times 2 = 2.9.$$
* * *
I have been working on this for a while now. As the example above demonstrates, the obvious greedy approach of selecting $Y_i$s with largest expectation does not work. I solved the special case of $k=1$ using dynamic programming. But my guess is that the general case is NP-hard.
Note that the value of of $Z_S$ depends on $S$ and the values of $Y_1,\dots,Y_n$: given $S$, the random process is that we randomly pick the values of the $X_1,\dots,X_n$, compute the values of $Y_1,\dots,Y_n$, then based on the values of $Y_1,\dots,Y_n$ we find the set $T$ of size $k$ that maximizes $\sum_{i \in T} Y_i$, and let $Z_S$ be the result (i.e., we let $Z_S$ be the sum of the $k$ largest values from $Y_1,\dots,Y_n$). This is why just choosing the $k$ $Y_i$'s whose expected value is largest does not yield the correct result.
|
https://cs.stackexchange.com/questions/37294/choosing-a-subset-of-binary-variables-to-maximize-the-sum-of-the-highest-k
|
[
"algorithms",
"complexity-theory",
"probability-theory"
] | 13 | 2015-01-16T13:41:23 |
[] | 0 |
Science
| 0 |
416
|
cs
|
Covering a complete graph with n copies of an arbitrary graph: NP-complete?
|
> Given a complete graph $G$, an arbitrary graph $H$, and a positive integer $n$, are there subgraphs $A_1,\dots,A_n$ of $G$ (not necessarily disjoint) such that their union is $G$, and each of them are isomorphic to $H$?
This is a problem which I believe is NP-complete, but I am unsure if it is actually so. Any ideas of how to prove this?
Notes:
* If $G$ is instead allowed to be an arbitrary graph, then this is clearly at least as hard as [subgraph isomorphism](https://en.wikipedia.org/wiki/Subgraph_isomorphism_problem), which is NP-complete.
* If $G$ is allowed to be an arbitrary graph, and $A_1,\dots,A_n$ are required to be isomorphic to a subgraph of $H$, instead of the entire graph $H$, then the problem can be reduced from [vertex cover](https://en.wikipedia.org/wiki/Vertex_cover) (which is NP-complete) by setting $H$ to be a [star graph](https://en.wikipedia.org/wiki/Star_\(graph_theory\)) with the number of spokes equal to the number of nodes in $G$.
* The problem where $H$ must also be a complete graph is called "covering design", and has some discussion [here](https://math.stackexchange.com/questions/1734855/minimum-number-of-subsets-of-a-of-a-given-order-that-contain-all-possible-pair), with closed forms for when $H$ has 3 or 4 nodes. Finding algorithm for this is apparently an open problem.
|
https://cs.stackexchange.com/questions/89221/covering-a-complete-graph-with-n-copies-of-an-arbitrary-graph-np-complete
|
[
"algorithms",
"complexity-theory",
"graphs",
"np-complete"
] | 12 | 2018-03-11T15:07:57 |
[
"Do you mean a subgraph by a subgraph induced by a subset of vertices of $G$ (which is the definition used in subgraph isomorphism problem)? How do you define the union of two subgraphs?",
"Another special case that looks hard (an open problem since 1967) is when $H$ is a collection of vertex-disjoint cycles: en.wikipedia.org/wiki/Oberwolfach_problem",
"@WillardZhan I didn't think about it before. (I mainly thought about cases where $H$ is nearly as large as $G$.) Let's say I'm interested in answers of either variant.",
"If $G=K_m$, is $m$ given in binary or unary?"
] | 4 |
Science
| 0 |
417
|
cs
|
Is extensionality for coinductive datatypes consistent with Coq's logic?
|
Given a coinductive datatype, one can usually (always?) define a bisimulation as the largest equivalence relation over it. I would like to add an axiom stating that if two members of the type are related by the bisimulation, they are equal in the sense of Leibniz equality (`=`). Would this make the logic inconsistent?
* * *
An example for streams:
CoInductive Stream A :=
| Cons : A -> Stream A -> Stream A.
CoInductive Stream_bisim A : Stream A -> Stream A -> Prop :=
| Stream_bisim_Cons :
forall x xs ys,
Stream_bisim A xs ys ->
Stream_bisim A (Cons A x xs) (Cons A x ys).
Axiom Stream_bisim_eq :
forall A xs ys,
Stream_bisim A xs ys ->
xs = ys.
* * *
My intuition is that this should be safe by analogy with functional extensionality, since it should not be possible to distinguish bisimilar streams by observation. But of course I'd prefer an actual proof (or at least expert testimony) to such informalities.
|
https://cs.stackexchange.com/questions/63197/is-extensionality-for-coinductive-datatypes-consistent-with-coqs-logic
|
[
"coq",
"equality",
"coinduction"
] | 12 | 2016-09-06T08:12:19 |
[
"The last paragraph of section 2.2.2 of Simon Boulier's PhD thesis \"Extending type theory with syntactic models\" (tel.archives-ouvertes.fr/tel-02007839) states that it is provable in a univalent setting, if you use a well-chosen definition of stream, and gives references.",
"@paulotorrens No -- I still believe that this is safe, but still don't know for certain. In practice, Coq's generalised rewriting makes using bisim instead of propositional equality bearable, so I would tend not to use the axiom.",
"One year later; did you manage to find the answer?"
] | 3 |
Science
| 0 |
418
|
cs
|
Regularity profiles
|
A standard exercise in formal language theory uses [Lagrange's four-square theorem](https://en.wikipedia.org/wiki/Lagrange%27s_four-square_theorem) to construct a language $L$ such that $L$ isn't regular but $L^2$ is regular. (Let $A = \\{ a^{n^2} : n \geq 0 \\}$. Then $A$ isn't regular, but $A^4 = \\{ a^n : n \geq 0 \\}$ is regular, hence either $L = A$ or $L = A^2$ fits the bill; in fact $A^2$ is not regular, so we must pick the latter.)
[This answer](https://cs.stackexchange.com/a/112357/683) generalizes this, constructing for every $m$ a language $L$ such that $L,L^2,\ldots,L^{m-1}$ are not regular, but $L^m,L^{m+1},\ldots$ are regular. This prompts the following definition:
> The _regularity profile_ of a language $L$ is $\rho(L) = \\{ n \in \mathbb{N}_+ : L^n \text{ is regular} \\}$.
My question is:
> Which regularity profiles are achievable?
The answer mentioned above shows that $\\{n : n \geq m \\}$ is a regularity profile for every $m \geq 1$.
It is also easy to construct a language whose regularity profile is empty: $\\{ a^{2^n} : n \geq 0 \\}$.
Clearly every regularity profile is closed under addition: if $L^a,L^b$ are regular then so is $L^{a+b}$.
> Is every subset of $\mathbb{N}_+$ which is closed under addition a regularity profile?
The question is interesting both for a general alphabet and for the special case of a unary alphabet.
|
https://cs.stackexchange.com/questions/113326/regularity-profiles
|
[
"regular-languages"
] | 11 | 2019-09-02T07:08:40 |
[
"@BaderAbuRadi I'm not aware of any progress on these questions, though I'm not sure I would know. Nobody contacted me regarding them.",
"Yuval, do you have an idea if these questions have been studied yet, or did they remain open?"
] | 2 |
Science
| 0 |
419
|
cs
|
(Slightly) faster simulation of quantum Fourier transform
|
Suppose I want to write a classical software simulator of a quantum circuit with $N$ qubits. When it comes time to simulate the quantum Fourier transform I can evaluate all $2^N$ states to determine the probability amplitudes, and then perform a Fast-Fourier Transform on the probability amplitudes in time $o(N 2^N)$. Finally in $o(2^N)$ time I can generate a scan of the partial sums of the probabilities of all the result states. Then I can choose a random number in the range $[0,1]$ and use it to do a binary search of the partial sums.
This results in a simulator that, each time is run outputs a single $N$ bit binary number with the probability distribution predicted by theory.
Can I do better? Of course I can't do exponentially better in general, but perhaps I could reduce the time to simulate a single experiment to $o(2^N)$?
I can do significantly better under some circumstances. For example, [Gilbert, Guha, Indyk, Muthukrishnan, and Strauss, "Near-Optimal Sparse Fourier Representations via Sampling", _ACM Symp Theory Comp_ , STOC-44:152-161, 2002,](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.135.7607) seems to indicate that if there are only $B$ frequencies (or if the $B$ frequencies make up "most" of the power of the signal) then there is a randomized algorithm that will recover all of them (and their amplitudes) in time, space and number of samples polynomial in $B$ and $N$.
I guess I'm hoping for something like that, but only to get one frequency, and to have some guarantee that the probability of getting a particular frequency will be proportional to the amplitude of its coefficient.
|
https://cs.stackexchange.com/questions/13325/slightly-faster-simulation-of-quantum-fourier-transform
|
[
"randomized-algorithms",
"quantum-computing",
"fourier-transform"
] | 11 | 2013-07-17T20:50:14 |
[
"suggest migrate to Theoretical Computer Science"
] | 1 |
Science
| 0 |
420
|
cs
|
Change in the distances in a graph after removal of a node
|
Given an undirected unweighted graph $G=(V,E)$ and a node $s \in V$, we are looking for a vector $\operatorname{diff}[]$, such that,
$$\operatorname{diff}[v] = \sum_{u \in V \setminus \\{v\\}}{(d^{G \setminus \\{v\\}}_{su}-d^G_{su})}$$
In other words, we are looking for the difference in distances from $s$ to every other nodes after removal of each node $v$.
Now the question: is there an algorithm with time complexity $O(n+m)$ that can calculate the vector $\operatorname{diff}$ for a given graph $G$ and node $s$? If yes, what is the algorithm (or the idea behind that algorithm)?
For a specific node $v$, we can run BFS on $G$ and $G \setminus \\{v\\}$ and find the $\operatorname{diff}[v]$ in $O(n+m)$, but here we want $\operatorname{diff}$ for all of the nodes.
I know that we can determine, whether $\operatorname{diff}[v] >0$ for every node $v$ (using shortest path tree of $s$), in $O(n+m)$, but is there an algorithm to find the exact value of $\operatorname{diff}$ in $O(n+m)$ time complexity?
**Hints.**
There are some properties in the shortest path tree that may help:
1. If we construct the SPT, and then add the other edges of the graph that are not in the SPT, there will be edges from one level to the next level, or edges among nodes within the same level.
2. When we remove a node $v$, only the distance between $s$ and the descendants of $v$ can be changed.
3. For a node $v$, if all the descendants have another neightbour in $G$ that is on the same level as $v$ in the SPT, then $diff[v]=0$.
4. For every descendant of $v$, if we keep track of the incoming edges whose other endpoint is in another subtree (subtree of siblings of $v$), we can easily update the distances for its children (Suppose that child is $v'$, the change in $diff[v]$ for such $v'$ will be $\min{(diff[v']+1,(d^{new}_{sv'}-d_{sv'})\cdot(\\# \text{children whose endpoint is in the subtree of }v)+(\text{new distance of nodes whose endpoint is outside subtree of v}))}$).
We can assume that the graph is 2-vertex-connected, which means that it will not be disconnected by removing one node (otherwise we can find all the vertex cuts of size of using DFS and check each connected component separately).
|
https://cs.stackexchange.com/questions/29746/change-in-the-distances-in-a-graph-after-removal-of-a-node
|
[
"algorithms",
"graphs",
"shortest-path"
] | 11 | 2014-09-07T20:47:48 |
[
"@FrankW If that distance goes through a child, then it will be the minimum is the first term $diff[v']+1$.",
"there are at least 3 papers by Camil on that page, & online paper links are not given so far. the papers generally look at adding/ removing vertices/ edges.",
"@vzn The paper by Camil investigates edge removal right?",
"suggest looking into \"online algorithms\" or \"incremental/ decremental\". seems like an online version of APSP eg online version of APSP tcs.se"
] | 4 |
Science
| 0 |
421
|
cs
|
Minimum edge deletion partitioning of a planar graph
|
I'm interested in the time complexity of the following problem:
Given an undirected _planar_ graph $G=(V,E)$ and a weight function $w:E \rightarrow \mathbb{Z}$ (so weights can be negative, too), color the vertices in such a way that the sum of the weights of the monochromatic edges (i.e. those between same color vertices) is minimized. There is no limit on the number of colors you can use. Note that it is not necessarily optimal to give each vertex a distinct color as negative edge weights are possible.
A version of this problem where $G$ is not restricted to be a planar graph is NP-hard (see [Minimum edge deletion partitioning](https://cs.stackexchange.com/questions/45372/minimum-edge-deletion-partitioning)) by a reduction from the vertex coloring problem. However, we cannot use the same reduction for the problem here because $G$ is planar.
Any hints, pointers, comments are welcome.
|
https://cs.stackexchange.com/questions/45731/minimum-edge-deletion-partitioning-of-a-planar-graph
|
[
"complexity-theory",
"graphs",
"np-hard",
"weighted-graphs"
] | 11 | 2015-08-31T06:00:04 |
[
"If you restrict the number of colors to 2, then the problem is equivalent to max-cut (with possibly negative edge weights), which is NP-hard for general graphs but solvable in polynomial time for planar graphs. So maybe planarity could help here as well.",
"The interesting property of planar graphs in this context seems to be that they are 4-colorable. As D.W. pointed out however, the optimum for your problem doesn't depend on using a minimum number of colors, so intuitively the planar restriction shouldn't affect the complexity. I have a hunch the reduction given by Dennis Kraft would still hold, because you're not considering the planar input graph coloring in isolation, but I might just as well be wrong.",
"I've edited the question to reflect your comment that the number of colors is unlimited. In the future, when someone asks a clarification question, please edit the question -- don't just leave clarifications in the comments, as people shouldn't have to read the comments to understand your question. The source of the confusion might have been: if edge weights are non-negative, and if there's no limit on the number of colors, the problem is trivial: just assign each vertex its own color. However in this problem edge weights can be negative, so the trivial solution isn't necessarily optimal.",
"No, it's not given.",
"The number of colors is given, right?"
] | 5 |
Science
| 0 |
422
|
cs
|
When can you "invert" an equation in the lambda calculus
|
Suppose that $M$ is a full model of the simply typed lambda calculus. Suppose each base type is infinite.
Now suppose that $f$ and $g$ are two functions in $M$ (not necessarily in the same domain) that are not definable by any pure term, and that $\alpha$ is a pure term of the $\lambda$-calculus such that: $$M(\alpha) g = f $$
My question is: when is it possible to find a pure term $\beta$ such that $$g=M(\beta)f$$
Are there easy to state necessary or sufficient conditions? I have been unable to find counterexamples when gs type complexity is higher than fs, so maybe that is a sufficient condition?
A couple of examples:
if $f$ is the converse of $g$: $$f=M(\lambda xyz. xzy)g$$ then we can find such a $\beta$ -- in this case, letting it also be $\lambda xyz. xzy$.
Similarly If $f$ is application to $a$: $$f = M(\lambda xy.yx)a$$ then $a$ is $f$ applied to $\lambda x.x$: $$a = M(\lambda y.y(\lambda x.x))f$$
Lastly, if $x$ is a variable in some base type and $f=M(\lambda xy.x)a$, then I don't think there is any pure term such that $a=M(\beta)f$.
|
https://cs.stackexchange.com/questions/57786/when-can-you-invert-an-equation-in-the-lambda-calculus
|
[
"lambda-calculus",
"combinatory-logic"
] | 11 | 2016-05-23T18:15:31 |
[] | 0 |
Science
| 0 |
423
|
scifi
|
Novel about an immortal man exposed by world government relates his life through history
|
I read the book from my local library in the early- to mid- seventies. It was hardcover (library bound) and the dust jacket had a printed burlap or canvas background. The back flap mentioned that the author's name was a pseudonym. The book had lots of conversation, anecdotes and opinions with little to no 'action'. I came away with impression that the author wasn't a professional writer, but rather more like a history professor with an academic reputation to protect.
It begins shortly after the formation of a world government, and the President of Earth is presiding over the trial of Earth's only immortal man, for the crime of withholding the secret of immortality. Much of the book is taken up by his narration of stories of his life, from his birth in prehistoric times to the present. This could almost be the backstory of 'The Man From Earth', but IIRC he was never a famous person.
One anecdote I remember is what he called 'Pavlov's Other Experiment', with the supposed discoveries by the scientist after the surprising results of the 1924 Leningrad flood. The novelist added a vitamin deficiency factor that became an important plot point. There was also a story I recall as being very amusing about a British military steamship in Egypt before or during the occupation in the eighteen hundreds.
And finally, as a major plotline (such as it is), everybody is taught the simple trick to become immortal. When dead people are cloned and become 99.99% similar, their soul and memories are reunited with their bodies and they are taught immortality; time-traveling robots collect DNA from everyone who has ever lived and they become immortal as well.
This is not Bixby's "A Man From Earth", Anderson's "Boat of a Million Years", Heinlein's Lazarus Long, Borges' "The Immortal", Zelanzny's "This Immortal". The main character was not a time traveler or the Wandering Jew. It is possible I'm getting the similarity thing confused with van Vogt's Null-A, but there was something like that.
The immortal man was likely 6000-8000 years old, and the time of the novel in a future not far from now. His prehistoric tribal roots being near the invention of agriculture? (maybe)
|
https://scifi.stackexchange.com/questions/66361/novel-about-an-immortal-man-exposed-by-world-government-relates-his-life-through
|
[
"story-identification",
"novel",
"immortality"
] | 59 | 2014-08-23T20:23:52 |
[
"The part about the protagonist being thousands of years old eliminates the novel Operation Longlife by E. Hoffmann Price. Doc Brandon, an obvious knockoff of the pulp hero Doc Savage, was less than two centuries old when the government realized he'd somehow stumbled across a method of keeping himself young and fit, indefinitely, and they very much wanted to persuade or coerce him to share his secrets.",
"@ImaginaryEvents Elements of it do sound hauntingly familiar, but then Time Enough for Love and This Immortal are a couple of my favourites so it's probably just that.",
"@Ash, no, the book was new and a complete novel, Perhaps I mis-capitalized 'other experiment', it was just how the character referred to it. I'm still hoping someone like yourself will recognize it or discover it.",
"The description you've given of the condition of the \"book\" in question actually sounds like you've found a single bound copy of a serial of some sort, it might be worth checking back catalogs from the like of Strange Tales and Omni for particular parts that stand out to you. But given that the title \"Pavlov's Other Experiment\" returns zero useful hits anywhere I can think of you may be out of luck I'm afraid.",
"@GorchestopherH Nothing yet. I will update here if I get the answer.",
"Have there been any updates on this on other sites?",
"Always worth mentioning what you've tried before so you can eliminate the obvious.",
"Thanks. There was a second reddit thread as well, but I tried to mention the top guesses above. reddit.com/r/printSF/comments/va9dz/…",
"I'm sorry. @Richard, what is obvious?",
"reddit.com/r/tipofmytongue/comments/wi3hk/… - Obviously"
] | 10 |
Life & Arts
| 1 |
424
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scifi
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Looking for science fiction assassination story with mysterious girl
|
For years I've been looking for a short science fiction story about a man who was released from a prison planet in order to assassinate a candidate for galactic president. He does this on a space station, and escapes with the help of a mysterious and very attractive girl with silvery hair and multi-colored skin.
I read this short story some 5-6 years ago online.
The assassin was released from the prison planet by some influential people so that he may assassinate the galactic president candidate, whose rule would, according to said people, be bad for the galaxy.
I also remember that the girl, who is actually a young woman is also a prostitute. The first time he sees her she's walking into the bar accompanied by another man. I don't remember why she helps him. She was likely his contact, given to him by those who sent him on the assassination.
They escape together after creating a diversion with an explosion, running off into some corridor that probably leads to a way off the space station.
The story story ends there but in my opinion leaves room for a sequel, even if only to explore the protagonists' developing relationship.
|
https://scifi.stackexchange.com/questions/27694/looking-for-science-fiction-assassination-story-with-mysterious-girl
|
[
"story-identification",
"short-stories"
] | 55 | 2012-12-06T11:39:59 |
[
"Jupiter Ascending? Which is a 2015 film, and not a short story I read somewhere in the early 2000s. I saw that film, and never even noticed any common plot elements. Sorry.",
"Sounds like Jupiter Ascending (imdb.com/title/tt1617661).",
"Aspects remind me of Spinrad's \"Agent of Chaos\". But that was a full novel and not a short story.",
"Hello @Moacir and thanks for trying to help me find this story. I looked up the index of that issue here (archive.org/details/…), but couldn't find a story by that author or by that name in 1983. Moreover, I found no place where a story by that name is attributed to that author.",
"Hello @Dovid, I've set a bounty on your question. If you remember any additional details, now would be a good time to edit them in.",
"Novels are often serialized in magazines.",
"To the best of my knowledge it was a short story, not part of a longer story. Although, as I said, it asks for a continuation. So I am not 100% sure. I read it online.",
"Are you sure it was a short story? Could it have been an excerpt from a longer story? Also do you remember if you read it in a magazine, book or online?"
] | 8 |
Life & Arts
| 0 |
425
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scifi
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Story about man unable to wake up from dream
|
I am looking for a story which I read a long time back but cannot recall the name. The plot line was:
In a futuristic world, there are dream parlors which provide sleep with dream services. The protagonist is a frequenter of them.
One day, it was found that he is unable to wake up after slipping into a dream. All efforts to wake him up fail, and he keeps on dreaming and sleeping but is medically fit otherwise.
He became a medical case study and was kept alive for centuries. By studying him a lot was learnt about hibernation and the code to interstellar travel in hibernation was cracked through that knowledge.
Eventually after a few centuries the government asked his custodians for justification for spending billions per century to keep him alive.
His custodians revealed that:
> he is the last person alive who is capable of dreaming. The entire human race has lost the capability to dream. So he should be kept alive as long as possible as a rare treasure to humanity.
|
https://scifi.stackexchange.com/questions/117737/story-about-man-unable-to-wake-up-from-dream
|
[
"story-identification",
"dreams"
] | 43 | 2016-02-08T02:42:15 |
[
"Sounds like a good story... Were there aliens/robots or anything?",
"Damn, I have read this before, but I cannot for the life of me remember the name of the story. I think it was a short story from an anthology by Heinlein, but I can't say for sure.",
"When was \"a long time ago\"? You may not remember exactly, but can you give a ballpark? What is a long time ago to one person may only be a handful of years to another."
] | 3 |
Life & Arts
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426
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scifi
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A space story about a desert planet and a cup of water
|
I read this story over 15 years ago. It is probably a lot older. I read it in Serbian magazine (Politikin Zabavnik) but I think that the language of the original is in English. It's a short story, less than two A4 formats long.
The story as I remember it is as follows:
A young man/boy (crash)lands on a desert planet. His only possessions are clothes on his back and a cup. Maybe a gold necklace, too, I am not sure about that. He reaches the biggest city on the planet.
The main trade and commodity on the planet is water. The richest families are those that have wells, people work for water, trade deals are made for water etc. The youth comes to the town and says to one of the smaller traders in water that he is thirsty and would like to buy a cup of water. There might be some flying robots that ensure that all the contracts are obeyed by killing anyone who tries to renege on the deal, I am not sure.
Anyway, the youth is not allowed to drink, not right now. Trader thinks he has nothing of value or something. A bigger water trader, as a joke, offers to sell the youth a cup of water. His fellow traders joke with him, tell him they would loan him a cup or something, because the youth doesn't have anything of value and would have to sell himself into slavery to survive on the planet.
I do not remember what exactly happened, but the end result is that all the biggest traders on the planet sign a contract with the boy. And it goes like this: a boy's necklace for one cupful of water. One cupful, nothing more. The arc words are: _What is the value of one cup of water?_
The end of story is this: the boy puts a drop of water into the cup. The cup opens up a bit then starts transforming, in fractal designs. It sucks all of the water in the city, maybe even in the whole world and that giant form of cup is floating in the air now, blotting the sun. Some of the traders get worried halfway, try to renege on the deal and are zapped by the robots. Once there is no more water and the cup stops filling, the boy laughs at now poor traders and asks them, "What is the value of one cup of water?"
It is very similar to the story about king that would give half of his kingdom for a cup of water and another half for some bread.
|
https://scifi.stackexchange.com/questions/79870/a-space-story-about-a-desert-planet-and-a-cup-of-water
|
[
"story-identification",
"short-stories"
] | 42 | 2017-09-28T09:16:06 |
[
"It was a kid's story-they read it to us in class back in the 2nd or 3rd grade-so this would put the book at least before 1990, if that helps anyone"
] | 1 |
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427
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scifi
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Futuristic world where reality is humanity's plaything and God is in a zoo
|
This is a novel I read in 2015. It was an older book. The cover was black and hardcover. Don't remember any specific details. The book was in English. I believe it was from the 1980s or ‘90s.
It was set in the future where the world is united as one.
I'll try to outline all the major events that I remember, in as much detail as possible.
The story begins with a prologue of how a mutant gene called "The God Factor" was isolated and subsequently researched to reveal it gave humans reality-bending powers.
The first few test tube babies born with the gene were horribly deformed and could only lift light objects with their mind. However, with every subsequent generation they grew stronger until they could manipulate events on a universal scale. They were fitted with microchips which gave scientists complete control over them.
Using these people humanity became an interstellar civilization. Thoughts and ideas are no longer abstract as people with the God Factor can bring them into existence. The world government brings into existence "God", a manifestation of the collective faith of people, and places him in a zoo.
To mock death itself, the human race increases the biological lifespan of all humans by a trillion years, reasoning that, with unlimited resources and a universe too vast, they need as many people as possible. And that's where everything starts going wrong.
The protagonist is a scientist who works under the guidance of the scientist who was a part of the team that originally created the God Factor babies. He gets involved in a riot where 50 people immolate themselves, seemingly for no reason. Similar riots spread globally and on human colonized planets. The protagonist discovers that the reality benders have been siphoning energy from other universes to provide to their own and the continuous transfer of energy has caused the membrane separating different universes to weaken which causes severe suicidal tendencies in exposed people. Over 75% of the world population dies in a week as even the GF people are affected causing them to go supernova when dying.
The protagonist rushes to try and build a "reality anchor". It had a fancy name but I can't remember it for the life of me. As the world delves into anarchy, he used "God" to power it and restore the world's reality to it's original state. Then he discovers that he is in the lab which his mentor used to work in while they were working on isolating the God Factor gene. The book ends with him in a dilemma of whether to destroy the project once and for all or let it proceed and try to influence events in the future.
It's an amazing book and much deeper than I outlined here. It's very long and very thrilling.
|
https://scifi.stackexchange.com/questions/203664/futuristic-world-where-reality-is-humanitys-plaything-and-god-is-in-a-zoo
|
[
"story-identification",
"novel",
"genetic-engineering"
] | 39 | 2019-01-17T20:42:52 |
[
"@NeoDarwin Does anything in this question of mine sound familiar? scifi.stackexchange.com/questions/14510/…",
"Reality anchor is in quotes because it had a complicated name. It's purpose was to anchor reality.",
"This got nothing",
"It is not this book",
"Very confident. I read it only 3 years ago and have searched for it myself for the past week. Only upon failing did I decide to ask here @John Rennie .",
"It seems this should be an easy find with such easily Googlable terms as the god factor, but I have to confess I've drawn a complete blank. How confident are you that you've remembered the phrase correctly?",
"@Broklynite His mentor used to work in a different lab and it's there they discovered the God Factor. I think the author mentioned that it's since being converted into an museum.",
"“Then he discovers that he is in the lab which his mentor while they were working on isolating the god factor gene” I think there is a bit missing from the middle of that sentence. And how do you mean that he discovers that he is in a lab he presumably used to work in? Was this hidden from him in some way? And is the idea that reality has been restabilized but questioning if it should go on, or that the restabilization is possible but should it be? Sorry, just trying to get some clarifications."
] | 8 |
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428
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scifi
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Old SF novel, set on a military ship, one character can't order spaghetti and meatballs because of sudden mid-voyage rationing?
|
This one is a real longshot. I won't be surprised if nobody can identify it. I read this book sometime in the early-to-mid-1980s. Science fiction novel, checked out from a public library, written in English, and I am pretty sure it was in hardback. Told in the third person, with multiple viewpoint characters, and a fairly serious tone -- not any sort of parody or satire, for instance. The problem is that I only remember _one short scene_ clearly. Here's how it went:
1. This part of the story -- perhaps most of the story -- is taking place aboard a large spaceship with interstellar range (military, I'm nearly sure) which is large enough to require a great many crew members (probably hundreds). I think there is some sort of interstellar war going on, or else one seems likely to break out at any minute, but I can't remember details of the larger plot. I'm _sure_ the crew of _this_ ship were all human -- but I don't remember if their enemies (or prospective enemies) were equally human, or if this was set in one of those futures where there are other sentient alien races with their own battle fleets.
2. In the one scene that I still remember pretty well, which I believe comes near the middle of the book (definitely not in the first chapter!), the viewpoint character -- who was not a major figure in the early chapters -- has just completed a long shift. I believe he's part of the Engineering Department. Now he wants to relax by eating a nice hot dinner.
3. He decides to splurge. Instead of taking whatever is standard-issue food aboard that ship, he is willing to spend extra to get one of his favorite dishes. I don't think it was regular money he would be spending, though. The implication was that, in order to keep the ship's galley from running out of all the best items too fast during a long cruise, the rules were set up so that you had to accumulate "ration points," or something similar, for the _occasional_ special treat. The rest of the time, you just ate something much simpler and cheaper, three times a day, as a way to keep your body adequately nourished. For the sake of argument, let's say that what this guy wanted was a big plateful of spaghetti and meatballs, with a certain type of salad on the side. (I don't swear that this is accurate, but I _think_ he was looking forward to spaghetti and meatballs.)
4. He punches his order into a computer terminal, knowing full well that his account has more than enough "ration points" (or whatever they are called in the ship's economy) to cover the special dinner he's been promising himself.
5. Nonetheless, despite how hard he has worked to accumulate those points which are supposed to be redeemable whenever you like, he gets an error message telling him his order _cannot_ be filled today because of some change in ship's policies. He throws a fit! (I don't mean literally going berserk, but he does complain loudly.)
6. I just _vaguely_ remember that there was some sort of problem with the ship which had caused the Captain, earlier that day, to approve some new rationing restrictions on various things as a reaction to "a state of emergency" (or words to that effect). I don't remember if this was because of lack of energy to make nonessential things happen, or because they were carrying too many people and couldn't create special meals on demand for everyone, or what. Apparently the character I was just mentioning had not gotten the word yet when he sat down to eat dinner. I think the scene I described was followed by another scene showing the Captain (and/or some of the other senior officers) talking about how a flood of complaints was already coming in from sailors who didn't know all the facts about the problems the ship was currently facing (or was expected to face in the near future?).
7. I don't remember a thing about the cover art or the author, but I can say that if this novel had been written by any of the Really Big Names of 20th Century SF who sometimes wrote stuff with a military-style setting -- such as Poul Anderson or Gordon R. Dickson -- then I would have expected to run across the book again, sometime in the last couple of decades, and I haven't. (And it _certainly_ wasn't written by Heinlein; I'm familiar with everything he published.) I'm also sure it _wasn't_ a "licensed novel" set in a preexisting SF universe, such as _Star Wars_ or _Star Trek_.
|
https://scifi.stackexchange.com/questions/145076/old-sf-novel-set-on-a-military-ship-one-character-cant-order-spaghetti-and-me
|
[
"story-identification",
"spaceship"
] | 36 | 2016-11-13T18:07:05 |
[
"Seems similar enough that it might be a duplication of this answered question.scifi.stackexchange.com/questions/286709/…",
"This makes me think of a story I read in which garlic has been restricted onboard a spaceship, not due to a shortage, but because the aliens who have infiltrated the ship are allergic to it. Our hero, in tracking down why he can't get spaghetti, uncovers the plot.",
"I wonder if this couls be part of the Fixup The Great Explosion by Eric Frank Russel, the last part of which is better known as \"...and then there were none\"?",
"Hmm, for some reason it makes me think of Tau Zero by Poul Anderson, but you say it's definitely not by him.",
"@Iolrus I have read Tactics of Mistake several times (although not in the last few years). I don't remember ever noticing a scene such as I described above, with a member of a starship's crew getting frustrated over his inability to redeem his \"food ration points.\" I think the story I asked about, two years ago, was mostly set aboard a starship during a long voyage. Cletus Graeme was the main POV character in Tactics, and spent most of his time down on the ground as a soldier outsmarting his enemies during campaigns on various planets. Hope you can find what I'm looking for, though!",
"I'm sure I have read this in the last year or two, in which case I think it might be \"Tactics of Mistake\" by the aforementioned Gordon R. Dickson. It's the only book that fits the bill and is on my goodreads list.",
"Worth a try I suppose 🙂",
"@Danny3414 -- I'm sure those are two different things. I first read a Seafort book (#3) in paperback in the mid-1990s. Since then, I've read most of the others. The story I'm asking about is something I'd read at least a decade earlier, in a hardback I had checked out from a public library. Of course, stories of people in spaceships having to carefully ration their food in emergency conditions have probably been done dozens of other times in the history of SF.",
"Are you certain about the dates you read this? It reminds me of one of the Seafort saga books by David Feintuch but they were in the nineties. In one of them a batch of their ship's stores have been contaminated by Fish like aliens and the ship has to go onto emergency ration reductions",
"Hm, okay, then you might try the Humanx Commonwealth series, by Alan Dean Foster. I mostly only read the Flinx and Pip story arch, but I did pick up another book or two from the rest of the series, so it might have been one of those.",
"Interesting suggestion. Way back around 1983 or 1984 (roughly), I read the original Foundation Trilogy, and then the recently-released Foundation's Edge. I've reread those stories at various times, but not for some years now. Off the top of my head, I'm not remembering a scene such I described in my original post, though -- not in one of the first 4 Foundation books. It wouldn't be in any later \"Foundation\" book; I'm sure they weren't even in print when I first read the scene I've described about getting an error message when trying to order a special meal aboard a starship.",
"I very, very vaguely remember something like this, and I think it was part of the Foundation cycle by Isaac Asimov. However, not 100% sure, and there are a lot of books in that series, so only a comment, but you might want to look into it. Most of the books are great reads!",
"It's funny, I was also thinking Stainless Steel Rat or Bill the Galactic Hero. But the scene I think you folks are thinking of was when the titular character gets on board a ship and is forced to eat (I think it was called) rat-puppies the entire voyage. A rat-puppy was a ration sausage that got poked with a knife and blew up large and self cooked. It was tasty enough the first time, but it was the only food available the entire way. While it does have a similar feel to the OPs question, I don't think it matches.",
"I did read The Forever War back around the mid-1980s, but I've read it again since, and it wasn't this. One reason I'm sure is that \"The Forever War\" was very much a first-person narrative focused on one character's experiences. The book I'm vaguely remembering was third-person, with multiple viewpoint characters.",
"I doubt it's The Forever War by Aldeman, but that book does have some scenes with food rationing and kilocalorie equivalences being used to purchase goods and food.",
"Regarding the Harry Harrison suggestion: I'm sure the book in question was not written as comedy/parody; it was more serious. That eliminates the first Bill, the Galactic Hero book (although I did check it out from the same library in the 1980s, and enjoyed it). Also, the book I want was written in third person, with multiple viewpoints -- that would help eliminate the Stainless Steel Rat books. (Besides, I'm positive I didn't read anything about Slippery Jim diGriz until years later! The library near where I lived in the mid-1980s didn't have any of his stuff.)",
"@Longspeak found the first one online, searched through it, no joy.",
"@SQB I was just going to suggest Bill the Galactic Hero, too. Pretty sure it is, but have to wait until I get home to confirm.",
"Rings a bell, vaguely. Could it be something by Harrison, either in his Bill, the Galactic Hero series or his Stainless Steel Rat series?"
] | 19 |
Life & Arts
| 0 |
429
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scifi
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Short story about a man in a madhouse who asks the guard for a cigarette and tells him his story about having swapped bodies before
|
I am searching for a short story about a man locked in a madhouse who swaps his body with the guard/doctor while he tells him the story about his own body being swapped.
I remember the following:
* The madman asks the guard for a cigarette and starts telling him his own story.
* There was some relative of the madman who had a miserable life and one day he took the madman for a chat to a gloomy place where he would perform the conjuring to swap bodies.
* When the madman reaches the end of the story, he has already swapped his body with the guard's and starts speaking as if he is in the corridor of the hospital and not in a cell.
* The madman, who is now the guard, tells his victim not to yell nor to despair for nobody will believe him. He tells him of the importance of the burnt offering which, in this case, was the cigarette and not to forget 'the words'. Then he takes the guard's car keys and drives away, leaving the guard locked in his cell.
I read this story in 2006. I searched google but the keywords hospital/madhouse take me to news and the keywords cigarette/burnt offering take me to religious content. I have no clue as to where was this story published.
Thanks in advance.
|
https://scifi.stackexchange.com/questions/223920/short-story-about-a-man-in-a-madhouse-who-asks-the-guard-for-a-cigarette-and-tel
|
[
"story-identification",
"short-stories"
] | 35 | 2019-12-03T05:39:17 |
[
"I, too, remember this story. I've been trying to recall the title for years now. I first read it sometime in the early 90s in a short story anthology I picked up while living in Brazil. I'm pretty sure the collection was published for ESL students, as I remember it was in the library of the language school \"Associacao Brasil-America\" where I taught for several years. For a while now I had been thinking I only imagined this story, until I saw your post! Just wish someone out there could remember the title . . .",
"The concept sounds similar to the A.E Van Vogt short story \"Dear Pen Pal\". In that one the story is a series of letters from an alien to an earth man. During the correspondence the alien performs a mind swap with the man, the last letter being written by the man (now in the alien's body). en.wikipedia.org/wiki/Dear_Pen_Pal",
"I read this probably before 1986 and certainly before 1992. Maybe something by Zelazny or Harlan Ellison or something in one of the Campbell awards books.",
"Sounds similiar in concept to the movie 'Fallen' (1998) link - but checking that I can't see anywhere that it was based on a novel...",
"I recall this story too. It trigger something... will try to remember. In the meanwhile I suggest you, with a very similar plot, the short story by Julio Cortazar, \"Lejana\" in his great \"Bestiario\": es.wikipedia.org/wiki/Bestiario_(libro)#Lejana",
"Can you remember when you read this? If it was new at the time? What anthology/magazine it may have been in if one of the reoccurring ones? etc. If so you can edit your question with this information."
] | 6 |
Life & Arts
| 0 |
430
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scifi
|
A story about a doctor who travels to a parallel universe to seek a cure for bubonic plague
|
Recent news has been reminding me of various things I've read about the black death, including a story I believe I only saw once, and never stumbled across again. I encountered it over 30 years ago, so I remember nothing of such details as character names. (Not even what city, in what country, it was set within.) I know it was a shorter piece of fiction, rather than a complete novel. I found it in an anthology I checked out from a library, probably no later than 1988. English language. I can't remember what else was in the anthology, nor what the overall theme may have been, but I'm sure it was **not** a collection of several stories by the same author.
* * *
**Plot Points**
1. The main character, whose viewpoint is presented to us in the third person, lives in the twentieth century, but not _our_ twentieth century. The history of western civilization veered off in a different direction some centuries earlier. (I can't remember just when the divergence was stated or implied to have occurred, but at least one language spoken by the protagonist is still comprehensible over here, on our side of the divide.) As we meet him, he is already an example of his world's version of a fully trained physician who is dedicated to his work. I _think_ he is called "doctor" as a result of his education at a reputable university, but he doesn't use the methods we normally expect of a modern doctor – no immunization shots, no antibiotics, no X-rays or other imaging equipment, and I don't think he has ever touched a microscope in his life – because all those things, and the theories behind them, don't seem to exist in his world.
2. In the protagonist's culture, the preferred method of treating the sick is the sort of thing I would associate with "witch doctors." Elaborate magical rituals involving chants and dances and so forth, I think. In some cases, dealing with some types of ailments, these methods have delivered a comfortably high success rate, which, presumably, is why these methods are now considered the correct way to practice medicine, and anything else is widely viewed (by physicians, anyway) as a complete waste of time.
3. Our hero is a maverick. When the bubonic plague hits the city in which he resides, and hits it _hard,_ he becomes convinced that it is caused by something which his magic spells are completely unable to cure – and he doesn't think any of his professional colleagues in the area are doing much better. He wants to use some "experimental" and "alternative" methods which are radically different from the "proper" procedures he had diligently studied in school. I can't remember exactly what his methods were, but I know that my teenage self thought they at least _resembled_ some of the measures which a real-world modern doctor might recommend if he were on the scene – assuming the modern doctor lacked access to antibiotics and other modern tools of the trade, such as I mentioned in point #1, but wanted to help as best he could, based on his knowledge of the germ theory of disease and other useful points.
4. There is an argument in front of some sort of authority regarding whether the protagonist should be allowed to inflict such time-wasting and unproven techniques upon his trusting patients. (I think the authority in question was a committee which was either partially or entirely composed of senior medical men.) He gets a partial victory – he is allowed to take responsibility for treating any plague victims residing in one sector on the city map. Public health statistics will be gathered from each sector, day by day over the next several weeks, to see if his methods appear to be making any difference at all.
5. That decision _sounds_ fair and reasonable – except that, in practice, one or more of our hero's "competitors" (other doctors, using the time-honored methods of treatment within their assigned sectors) start _cheating._ Some weeks after that policy decision was made, the protagonist is told by one of his loyal assistants that a lot of dead bodies of plague victims are turning up _just inside_ the boundaries of the hero's assigned sector, and it's pretty obvious that at least one other doctor is having fresh corpses loaded onto wagons and dumped along the fringes of that sector in the middle of the night so that their fatality rates look lower, and his look higher.
6. The protagonist finally tries something completely new. This is another area where my memory fails. _Somehow,_ he has gained access to a magic spell that could let him travel from his world to a parallel world where history followed a different path. I think he needs other people to help by chanting portions of the spell, making certain gestures or dance steps, etc., to make it work properly. He can't just cast it on himself. I don't remember where this spell came from, nor why it had rarely (if ever) been used before. The doctor puts it into effect and vanishes into thin air.
7. At this point, the story stops showing us his viewpoint, and we start reading a formal report written by a professional medical man in what appears to be _our_ world. The report tells us that a strangely-garbed man was found in the streets of their city (our world's equivalent of the setting of the previous scenes, I believe) and was quickly diagnosed as being feverish from a serious case of bubonic plague. He was taken to a hospital and pumped full of antibiotics. Physically, he made an excellent recovery, but he kept saying nonsensical things about world history, about his own alleged medical training and preferred techniques, etc., which made no sense to anyone else, and so he was placed in the psych ward for a while. The plan was to figure out how deep his mental problems ran – was he delusional as a regular thing, or just temporarily having trouble distinguishing between "reliable memories" and some elaborate hallucinations which he might have experienced while delirious with that fever, or what?
8. The author of the report notes that after landing in the psych ward, this mystery patient became acquainted with the other mental patients and then started doing some "magic" nonsense, with ritual gestures and chants and so forth, which he loudly claimed could "cure" the afflictions with which they had been cursed. (I don't remember for sure, but _he_ may have claimed he was "casting out demons" or something along those lines.) The report-writer assures his intended readers that while several of the mental patients do, in fact, appear to have been acting much more lucid and well-adjusted since then, it must be a coincidence. The painfully obvious implication (to us, knowing what we know) is that the protagonist does, in fact, know some "magical" techniques which somehow can make a huge difference in treating cases of paranoia, schizophrenia, etc. In other words, _both_ worlds could benefit enormously by having the members of their respective medical communities compare notes and maintain an open mind about anything that seems "crazy" at first glance.
9. Again, my memory fails: I can't remember how the story ends. Specifically, I don't know whether the protagonist finally managed to get hold of a stash of antibiotics, etc. which would allow him to make a huge difference in treating plague victims after he carried those modern assets back home via another use of the same spell. (Note: As I was about to post this, it suddenly occurred to me – but I'm not sure if this is a genuine memory or a wild guess – that the protagonist _may_ have somehow persuaded several of his fellow mental patients to each perform one role within the coordinated team effort that is required to reverse the travel spell and send him right back to his native timeline with his new knowledge and medical supplies. _Maybe._)
* * *
Does anyone else remember reading this?
I did a little Googling before I took the trouble to type out all of the above, as well as searching through previous questions on this very site. I kept coming up with references to various full-length SF novels that gave lots of attention to the historical black death, and/or alternate-timeline variations and their aftermaths, but these novels definitely are not related to the much shorter story I had in mind.
So the reject pile – the list of things not to bother offering as "answers" – includes all of the following:
* _The Years of Rice and Salt,_ by **Kim Stanley Robinson.**
* _Doomsday Book,_ by **Connie Willis.**
* _The Plague Tales,_ by **Ann Benson.**
* _The Crystal Empire,_ by **L. Neil Smith.**
* _In High Places,_ by **Harry Turtledove.**
* _Any_ of the novels and shorter stories that were ever published as part of **Randall Garrett's** "Lord Darcy" series. (Not all of them written by Garrett.) Those tales were set in a parallel universe where most technology is lagging a century or more behind ours, but medical treatment is largely a matter of using psychic healing techniques which _frequently_ succeed. At one point, a sorcerer spoke disparagingly of the superstitious fools who think applying some moldy old bread to a fresh wound can somehow keep it from getting a nasty infection. (After all, what good did mold ever do anybody?)
|
https://scifi.stackexchange.com/questions/230744/a-story-about-a-doctor-who-travels-to-a-parallel-universe-to-seek-a-cure-for-bub
|
[
"story-identification",
"short-stories",
"alternate-history"
] | 33 | 2020-05-02T21:28:52 |
[
"Nourse did write at least one story about the plague but it has a very different plot.",
"0 I have read this story and remember it. I am 80% certain it was a short story written by Alan E Nourse, who wrote lots of medical sci fi stories. Hunted through my collection to see if I can locate it but annoyingly, I cannot find it in any Nourse collection. If not him, it was a contemporary like Blish...but I still think it was Nourse. I recall the story very clearly.It doesn't seem to be JAmes white either.",
"S/what related to The Hertford Manuscript, a sequel to H. G. Wells' The Time Machine by Richard Cowper: the protagonist gets stuck in 1665 London and attempts to direct public health measures against rats, eventually getting infected.",
"@user888379 I'm very familiar with all three, but I hadn't really thought of connecting them to this one. \"Wheels of If\" probably comes closest -- it deals with going \"sideways in time\" to where it is still \"the same year,\" but history took a different turn centuries ago, instead of just people or artifacts from a better future coming back to the 20th Century. Also, the other two had tragic endings. Although in \"Wheels of If\" I was never convinced that it was perfectly all right for the main character to deliberately leave his analogs stranded in each other's bodies in other timelines.",
"This feels familiar, but it may just be that I'm reminded of aspects of de Camp's \"Wheels of If\", Moore's \"Vintage Season\" and Kornbluth's \"The Little Black Bag\" - I could imagine it having been published in \"Unknown Worlds\" or \"Astounding\" in the '40s."
] | 5 |
Life & Arts
| 0 |
431
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scifi
|
SciFi Short Story about an immortal man digging through an asteroid to meet a woman
|
Short story from the 80's or 90's, I saw someone asking about this on another forum but never got an answer. I've been curious ever since.
The story is set in a decadent future where everyone lives forever and mostly they go to parties. Guy meets a girl at a party, suggest he start at one side of an asteroid and digs a tunnel by hand to her, while she waits in a hollowed out space and creates a beautiful garden while waiting (robots take care of all mundane life support stuff).
So he digs for 100 years, makes it through to her chamber, they have a long romance, and when they've had enough they go back to civilization. The robots bury everything and return the asteroid to the way it was. Then they run into each other at a party and she overhears him proposing it to a different girl. That's when she says, "You've done this before."
This is the original post, for those curious (though I've reposted all relevant info): <https://www.reddit.com/r/tipofmytongue/comments/21004u/tomtscifi_short_storyeveryone_lives_forever_man/>
|
https://scifi.stackexchange.com/questions/120302/scifi-short-story-about-an-immortal-man-digging-through-an-asteroid-to-meet-a-wo
|
[
"story-identification",
"short-stories"
] | 30 | 2016-02-22T23:57:46 |
[
"That's not a knife, that's a spoon!"
] | 1 |
Life & Arts
| 0 |
432
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scifi
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A man sent to a parallel Earth to save someone important
|
This is not a novel, but "longish" short fiction, novelette or novella. I read it around 1984, in English, in an already used collection containing half a dozen or so stories.
A man, on our Earth, is contacted by a bizarre agency that offers him to get his mind transferred to a body in an alternate Earth, in order to save, either some polity from an external enemy, or the queen of some polity threatened by an "internal" cabal. Why he accepts is not clear, since when will he be able to use the money he is offered? No return seems promised.
He gets there, and meets several species of humanoid beings. They all have names that contain the word "man" in the local language, but I forgot how that sounds. Somehow, the agency that hired him managed for him to understand the language of the species he was supposed to help (otherwise, he would have been useless!) When he finally meets them, they tell him the names of all the other species, from his descriptions. And the names were translated into English for the benefit of the reader. This is how I found out that the second part of the name, common to all species, meant "man". Note that this is a "reconstructed" answer to Valorum's question in a comment, not a direct memory. An alternate possibility is that the language capabilities he must have received from the agency that hired him included the words for man, snow, cave and water and he invented the name of the species in the local language himself, but it is rather unlikely.
* One species is a "Snow-man", a huge and frightening Yeti (but not the most aggressive species in that world) who lives in the eternal snows of a high mountain range (or polar cap?).
* Another is a "Cave-man", without eyes because they live in deep caves with no light.
* A third one is amphibious, "Water-man" or "Sea-man" or "River-man", I forget which.
* One species practices cannibalism, and they file their teeth better to tear flesh. I forgot if it is one of the latter two, or still a fourth one.
* Finally, the ones he is supposed to help are essentially like us.
Our hero crosses all these obstacles, reaches the polity he has been hired to help, and saves the queen from the cabal, or possibly the entire polity from the enemy. I don't remember the end well, but he never goes back to our Earth.
|
https://scifi.stackexchange.com/questions/211068/a-man-sent-to-a-parallel-earth-to-save-someone-important
|
[
"story-identification",
"parallel-universe",
"novella"
] | 29 | 2019-04-28T10:07:19 |
[
"@MadPhysicist Very funny. I was referring to en.wikipedia.org/wiki/Graphic_violence IIRC the scenes with the cannibals did involve some violence and some blood, but well within the very moderate criteria of SF at that time. So as I understand this wiki page, they was no \"gore\".",
"@Alfred en.m.wikipedia.org/wiki/Al_Gore",
"@Valorum If by \"gore\" you just mean a lot of blood, well, when he met the cannibal species, there were maybe some scenes with a lot of blood. But not \"gore\" in a sense of something really offensive, disgusting. As a Frenchman, I am not completely clear about the meaning of \"gore\".",
"Re: phrases : no, alas, I don't remember any phrases.",
"@Valorum Re: sexual content. I cannot vouch that no discrete allusion to sexual contact was mentioned. But if it was, it would have been in the very, very subtle way such topics were treated in SF of before 1990.",
"@Alfred - That needs editing in. Also, can you recall any specific phrases used in the story?",
"@Valorum When he meets the final species, the one closest to us, and understands their language (the agency that sent him probably arranged this, otherwise how could he be of any use ?) they tell him the names of the others species and also their meanings. That's when the reader finds out.",
"@Alfred - I don't understand the man part. If it was in the local language, how do you know it meant man?",
"Re: \"Cave-man\", \"Snow-man\", \"polity\" No, the words were definitely not there. I used \"polity\" since I did nor remember whether it was a realm, an Empire, a republic... As for the words in \"man\" I wrote that all the species names contained the same word which meant \"man\" in the local language, and the other half of the name was \"snow,\" \"cave\", \"water\" or \"sea\" also in the local language.",
"@Valorum No, not at all. It was in a collection of SF and Fantasy, very typical of the genre. Until I had checked all the collections containing Nightwings before 1985 that Jenaya suggested, I did consider the possibility both were in the same collection",
"You've put a bunch of words in quote marks (\"Cave-man\", \"Snow-man\", \"polity\"). Are these words that you recall as definitely being in the novella?",
"@Alfred - Did the story contain explicit language/gore/sexual content?",
"@Valorum I read it in English. As I have written, I found those two collections in a hotel in the US. And I am sure that it was not in the same collection as Nightwings. Well, it does not hurt to make the language explicit !",
"@Valorum I tried to remember more, but that was very long ago, and rereading my question, I was unable to add anything more.",
"Instead of just sticking bounties on, why don't you go through the the checklists here and improve the question? I'm sure you can add at least one extra piece of detail that's not already been mentioned.",
"@Pastychomper thanks Monica Thanks for your help, but I listened to a few chapters of \"Quest of the Golden Ape\" and it is definitely not my book.",
"This sounds a bit like \"Quest of the Golden Ape\" by Randall Garrett, Paul Warren Fairman and Adam Chase. That had a man transferred to an alternate Earth with several divergent human species, I think one was cold-adapted, and his mission was to save one of the races (including a Fair Maiden™) from a brutal conqueror. He was an exile raised secretly on Earth though, and took his body with him. Might be worth trying those authors in case what you read was a sequel.",
"@Alfred The thing about old memories is that they can get mixed up. Look up the other stories in that Galaxy anthology and maybe other details will pop out.",
"@Spencer a) the stories in the collection containing \"Nightwings\" were by several authors, but I checked the entire list of publications of \"Nightwings\", thanks to Jenayah and did not find my story; it had to be in a completely different collection, that happened to be on the same bookshelf in that hotel b) the details of \"The Sharing of the Flesh\" do not match my memories at all",
"There is cannibalism in \"The Sharing of the Flesh\" by Poul Anderson, which was in The Eleventh Galaxy Reader along with \"Nightwings\".",
"Do you remember whether the stories were by different authors, or were they all by Robert Silverberg?",
"@Jenayah Thanks so much for the list you sent me. Alas, I tried all the different books (I did not yet check every single one of the lines that had the same title but different editors or publishers). None of the novellas and novelettes (it is clearly not a short story) in those collections seemed to be the right one. In fact I now believe that there were at least two different collections in that hotel, probably both of the 70's, Nightwings being in a different one than the one I am looking for.",
"For what it's worth, here is a list of the publications \"Nightwings\" appears in. If you can take a look, see if jogs any memory :-) and if you find it, don't hesitate to post it as a self-answer in the field below.",
"@Stormblessed Thanks for the guide (and your own edit !). Where did my comment disappear ? Well, once more. There is really nothing more that I remember about the story itself. But the connection with \"Nightwings\" is a time indication even if there were in two different collections, I really don't remember. It is the first time I ask about it on a forum, I did try to find it by myself by looking for it with keywords, but to no avail.",
"Hi, Alfred! If you want to improve this (already very nice) question, see this awesome guide!"
] | 25 |
Life & Arts
| 0 |
433
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scifi
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Short story about an elite that has mentally regressed due to assistive AI technologies
|
I came upon a comment describing a scifi short story where reliance on technology meant to improve appearance and demeanor has led to mental regression and AI control of the upper class that employs it. Unfortunately, I only have the following description to go on:
> I'm reminded of a Nebula(?) Award winning short story about hive-rats interacting with nobility in the 'future'. The nobility is shrouded in apperance/voice/stim tech such that the AIs are more the person than anything. A princess is brought to the under-city by her father to a shop that can fix the princess' tech, as it is malfunctioning. The daughter of the shop owner tries to peer into the princess' life and psyche as the shop owner tries to fix the princess. The princess has implants that stimulate her face, voice, and body to say the right things at the right times, to move the right way, that changes her face via lightsheets to be most beautiful to the observer she is with, that causes her to say just the right thing at just the right time and be increbily witty. But the daughter of the shop owner tries to peer through the tech to see the woman behind the veil. She discovers that the person behind it all is nearly mute and has the intelligence of an infant. The tech had been installed before ego formation and the person behind it all didn't really exist. She discovers it is also true of the man that brought the princess down to them too. The entire nobility is essentially faking it.
|
https://scifi.stackexchange.com/questions/216852/short-story-about-an-elite-that-has-mentally-regressed-due-to-assistive-ai-techn
|
[
"story-identification",
"short-stories"
] | 29 | 2019-07-31T04:37:14 |
[
"\"The Girl-Thing who went out for Sushi\"? Pat Cadigan, won the Hugo award for best novelette in 2013. Doesn't match all the details perfectly though.",
"You've rekindled a memory - I have definitely read this story! But I can't for the life of me remember the name nor author. I hope you find the answer. I'll have to look through my past readings, but unfortunately I'm better at remembering novels than short stories . . .",
"I've taken a look at the nebula winning list, but haven't seen nothing about it :(",
"That's the one, but here's a link to the comment directly. I wasn't sure if I could use links on a brand new account.",
"Presumably this is the original source - about a fifth of the way down the thread."
] | 5 |
Life & Arts
| 0 |
434
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scifi
|
Old sci-fi short story about buying an android?
|
Long, long time ago I came upon a collection of old (pre 1980s?) short sci-fi stories. I'm not 100% sure, but something makes me think they were by Russian authors.
One of them was about a woman, who lives a lonely life in her flat. She decides to buy a male android. There's an android factory where you can choose your android's characteristic. First she chooses the 'basic' version, but is unhappy, because it lacks any specific character. She sends him to a factory so that they can improve his character. She's happy for some time, but soon she finds out he doesn't have his own opinion. She resends him to a factory and they improve him again. Again, she's happy for some time, but she finds out that the android doesn't have a free will and his feelings to her are programmed, not 'true'. Again, she sends him to the factory. They warn her that the android having a free will can do anything and might as well not return to her at all. She's determined to do that anyway. She sends him to the factory and waits in her flat for his return. At this point the story ends; we never find out whether the android came back to her.
I can't remember neither the title nor the author and I'm not able to google it. Can someone help, please?
|
https://scifi.stackexchange.com/questions/63197/old-sci-fi-short-story-about-buying-an-android
|
[
"story-identification",
"short-stories",
"androids"
] | 28 | 2014-07-13T13:24:36 |
[
"this may help you en.wikipedia.org/wiki/List_of_fictional_robots_and_androids",
"Not Asimov's Satisfaction Guaranteed?"
] | 2 |
Life & Arts
| 0 |
435
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scifi
|
Aliens secretly use video game to get humans to solve their problems
|
I recall a story probably 20-30 years ago (pretty sure it was a short story) in which a top gamer hears about a new computer game out that no one can beat. So he gets it and starts playing it. (Pretty sure it was before the age of playstation & x-box so it might be even older)
IIRC the game had little or no intro or rules explained. You start the game and have to figure it out.
It was an astronomical space battle puzzle. You launch your ship from a planet orbiting a sun in a binary (trinary?) system, and have to leave the system. But he finds if you boost to long, or to hard, ships from other planets (around the other stars?) will detect you, intercept, and destroy your ship.
So he starts playing and trying different things, and then goes power gamer mode, playing non-stop on caffeinated drinks and snacks for a couple days and finally solves it. I think it was by doing low powered gravity assists on a couple planets and looping around the suns a couple times until he builds up enough speed to escape the solar system.
At which point the perspective pulls back to that of a few aliens in their ship who are viewing his solution. They are amazed at his solution and how fast he solved it. They reveal that this is an actual problem they have been working on for months(?) and one of them races off to tell the crew of the real ship (a spy ship?) how to escape detection by the enemies and leave the system.
Then one of the aliens says something like, "You know, we have been having trouble planning the ground assault on xxxx planet, Maybe we should make another new computer game for the humans."
EDIT: Thinking about it now, I think I can vaguely recall an illustration of a figure-eight path the ship makes around the suns. Making me think, it might have been published in a Games or Computer Games magazine. Which would make me think it might be as old as the 1980s. (I read a lot of these in the 80s)
Its also possible it might have been in a SF&F stories magazine, although I did not read many of those except for OMNI.
|
https://scifi.stackexchange.com/questions/253816/aliens-secretly-use-video-game-to-get-humans-to-solve-their-problems
|
[
"story-identification",
"short-stories",
"aliens",
"computers"
] | 28 | 2021-09-14T22:10:07 |
[
"Vinge's The Peace War has an orbital mechanics game , but no aliens",
"Last Starfighter had a weaker variant of this.",
"While Pegman is a similar story (Aliens use humans to solve their problems by playing a video game) it is not the story I was thinking of. And a glance through Peace War it did not involve Aliens that I saw.",
"This almost sounds like a combination of Rudy Rucker's \"Pegman\" (aka \"Pacman\") about humans and aliens using video games to get clever solutions to problems rudyrucker.com/transrealbooks/completestories/#_Toc15 and Vernor Vinge's \"The Peace War\" in which there is a video game about orbital maneuvers",
"Oh ok, sorry for the confusion, I wrongly assumed it was a video you were looking for :)",
"But I am looking for a Short Story (or maybe novel) not a Movie.",
"That’s what I originally thought when I started to read your description, but I remember another one: “the bishop of battle” where a kid is managing to go through a level no one else managed to beat in an arcade, check that one out",
"Nope not it, though that sounds very similar to \"The Last Starfighter\".",
"I remember a movie with an arcade game where the character was in wireframe and the human managed to beat it, bringing some solution. It was a blue/cyan wireframe face talking. Does that ring a bell?"
] | 9 |
Life & Arts
| 0 |
436
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scifi
|
70s book/short story, Man wakes up from suspend animation or cryo and world has collapsed
|
In the book, the protagonist wakes up from either suspended animation or cryo (Probably supposed to be a short test), After 10-20 years have passed.
He finds the facility abandoned (and looted?), gets to the surface and it looks like a war zone. Wreckage everywhere, smashed buildings, bullet holes everywhere. (I think he gets some gear from the facility, MREs, Water, First Aid kit, Weapons) and goes exploring to find out what happened.
He comes across a (young kid?) who is terrified of him, (maybe trapped or pinned under debris), gives him food and water and digs him out or helps him so the kid trusts him. Eventually the kid leads him to his family (mother & other siblings) who are equally terrified when they see him, but the kid convinces them the protagonist is OK, that he saved his life.
None of the children are really old enough to remember anything from before the protagonist enter the cryo test, but the mother is. He starts questioning her about what happened while he was asleep. She tells him it was NOT another country invading, it was all internal (society collapsed, food shortages, massive riots).
Later, I think they hear a large group of people approaching the (town? city? area?) where the family has been living, and the family becomes frightened again, saying the enemy is coming back.
He says he will help defend them and asks what the enemy looks like. She looks at him and says "They look just like you." He is African American, the implication being that African-American uprisings are what caused the riots and collapse of society.
This might have been a short story/novella. It probably was a paperback in English published in the USA.
I may be misremembering, maybe she did not tell him they look like you, he just went and got into a position to defend against the enemy, and when they approached, realized they were all African-American.
|
https://scifi.stackexchange.com/questions/185987/70s-book-short-story-man-wakes-up-from-suspend-animation-or-cryo-and-world-has
|
[
"story-identification",
"short-stories",
"post-apocalyptic",
"suspended-animation"
] | 27 | 2018-04-19T23:18:42 |
[
"I wonder if this is one of Octavia Butler’s novels? Or a confused misremembering, perhaps of the Clay’s Ark series?",
"@AcePL Your probably right, I maybe miss remembering tYotQS.",
"@OrganicMarble - I vote for your proposition. Except for suspended animation it all adds up. And description of the device to travel in time, in the book, can be misleading. I will lay this on OP misremembering some details. I red the book, pretty sure this is it. Otherwise plagiarism...",
"Sounds very similar to the starting scenario of the RPG - Aftermath! addon - Operation Morphus: Operation Morpheus is designed as a campaign introduction to an Aftermath! world. The setting is a major university in an important city. The players take the parts of people having volunteered to take part in a ‘short-term’ experiment in cryogenic suspension, only to awaken many long years after the planned time. They find the world in ruins and have no idea of the cause of, reans for, or history of this disaster. Naked and unarmed, they must face a strange new world.",
"Your right it is very close. But I don't think its the book I was thinking of. In \"tYotQS\" when the woman tells him everyone is afraid of black men, he hardly reacts to it. (Cause he still thinks he will go back to his own time soon) I am sure in the book I was thinking of, it was a big shock to the protagonist when he found out why everyone was afraid of him.",
"This is somewhat reminiscent of \"The Year of the Quiet Sun\" but it's a time machine instead of suspended animation. The near-future race war in the USA matches."
] | 6 |
Life & Arts
| 0 |
437
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scifi
|
Old SF novel about Earth as a prison planet; newly arrived convict has a secret agenda
|
I think I read this no later than the year 1986. English language, hardback, available in a public library in Indiana in the mid-1980s. I don't think it was by any of the Big Names of 20th Century science fiction, or else I would have run across it again by now. It was a stand-alone novel; no cliffhanger ending, and no indication it was intended as part of a series.
The novel is written in the third person, with the emphasis on the thoughts and actions of the male protagonist. I _think_ his thoughts were the only ones we saw throughout the entire book, but I could be forgetting something. Here's what I remember about the plot.
## Plot Points
1. As the novel starts, we are seeing Protagonist (as I call him) arriving by spaceship to begin his prison sentence -- which I believe is meant to be the rest of his life, however many years that may be. I don't recall him thinking anything along the lines of "if I just keep my nose clean for the next ten years, I can get parole!" I can't remember what Protagonist was supposed to have done. I seem to recall that this prison planet is a future version of Earth. If I'm right, then the planet is no longer densely populated with billions of people cluttering the place up. More of a sparsely populated "wild frontier" area. But I don't recall what reasons were given for the fact that the prisoners were basically the only people in sight, such as a nuclear war a few centuries earlier, or some other catastrophe.
2. Most of the novel is set near where Protagonist is dropped off. I think it may have been stated or implied that the area where the ship landed was the only functioning spaceport on the entire planet. I think the spaceport and the nearby town are in the foothills near the base of a mountain range (and I keep thinking of Colorado in particular, but that may just be because my family moved to the Denver area not long after I read this book). I think a lot of the local prisoners work at some sort of mining activity in the neighborhood -- although I'm pretty sure that they are not "prisoners" in the sense of being locked up in cells every night; just in the sense of being stuck on Earth and not allowed to leave. I don't clearly remember this, but I suspect that there was some economic incentive, such as: "We will trade you consumer luxuries from offworld in exchange for how much of Substance X" -- meaning whatever the heck they were mining -- "you have to offer when we make our monthly visits in a starship." (I don't swear the visits happened each month; that's just an example.)
3. Soon after arriving, Protagonist meets a girl. I am almost certain that she is no more than 14 years old -- not prepubescent, but younger than a leading man's girlfriend/love interest/etc. would normally be in modern literature. (No, they don't end up sleeping together.) She seems to be going out of her way to get his attention -- she is intelligent, headstrong, aggressive in the way she speaks to him, and I _think_ she comes across as a something of a smug know-it-all. (Granted, if she's been here for years, whereas Protagonist has just arrived, then she has considerable justification for feeling that she knows a great deal more about local conditions than he does.) I don't remember if the girl is stated to have been born on the prison planet, or if she was brought here with her parents, or what. (I strongly suspect that she had not committed some terrible crime at, let's say, the age of 10 or 11, and been sentenced to spend the rest of her life on Earth as punishment for her own sins. I don't remember getting a "hardened criminal" vibe from her, but these memories are at least a third of a century old.)
4. At some point, it is hinted and then stated that the girl has some unusual ability. I'm thinking something "psychic," but not necessarily being able to telepathically peek into protagonist's mind and know exactly what he is thinking.
5. It also becomes clear, somewhere along the line (not in the first few chapters, I'm pretty sure), that Protagonist has a hidden agenda. Perhaps his conviction of a major felony was a fraud, and he's actually the future equivalent of "an FBI agent going deep undercover." Perhaps he really did do whatever he was accused of, but he wanted to get caught and convicted as part of a deeper plan. (Similar to the starting premise of the much later TV series _Prison Break,_ but that's just a guess.) Perhaps someone has offered a convicted man "a deal you can't refuse." But at any rate, he's not just another thug hoping to find a way to "settle in for the long haul" as part of the local society; as I recall, he hopes to someday get off Earth and be a free man again, if he plays his cards right. Protagonist appears to be sneaky, determined, an excellent fighter, and so forth. (Sort of like what you'd expect from a military commando type, although I don't remember if he had any formal military training from his pre-prisoner days.)
6. Protagonist comes to realize that a big shot in the prison colony has some sort of secret deal going on. I _think_ with some non-government faction that has its own starship for making covert visits to the prison planet as part of some high-stakes plan. Somehow, Protagonist (probably with the help of the girl) foils their diabolical scheme -- whatever it was.
7. The story was written in the fast-paced style of an adventure novel. We didn't have anyone holding up the plot for several pages at a time to give lengthy lectures on sociopolitical theory or economic strategy or anything similar; we followed a "lone wolf" from one interesting scene to another. I think this book was pretty short; i.e. not much more than 200 pages (or maybe even less).
8. In the last few pages, there's a scene where Protagonist and the girl are having another conversation, and she deliberately says something to tease him, taunt him, or something like that. I don't remember the wording, but it was obviously meant to get under his skin. He suddenly gives in to an impulse and grabs hold of her and pins her down on the ground, and she suddenly seems scared. He may or may not give her one quick kiss before he suddenly lets go of her, backs off, and says dryly: "Try that approach again in another five years, and you might manage to seduce me." I don't remember what she says or does then, but the implication is that him grabbing hold of her for a moment is, in fact, something she was kinda hoping he would do; since she doesn't say a thing to contradict him on that point. (I think she may even laugh at the realization that he had seen right through her.)
9. My impression is that Protagonist is about to leave Earth on a ship during the scene I mentioned in the previous paragraph -- he is in a very good mood because, somehow, he has "earned a pardon" or "is being brought in for debriefing" or "has gained access to a starship" or in some other way is heading offworld for a while. I don't remember if the girl is staying behind by choice, or if she'll be sent off to a nice school for a few years, or what. But his remark about "seducing me" indicates at least the possibility of a romantic happy ending for both of them at some future time.
So! Does anyone think all this sounds familiar? I'd like to refresh my memory of it and see what I think of the writing style after all these years.
* * *
P.S. To save you some time, here are a few "prison planet" or "prison colony" stories which this book definitely was **not.** (Although I read most of them around the mid-to-late 1980s.)
* "Coventry," by **Robert A. Heinlein**.
* _The Status Civilization,_ by **Robert Sheckley**.
* _Police Your Planet,_ by **Lester Del Rey**.
* _The Escape Orbit,_ by **James White**.
* _The Beyond,_ by **Jean** and **Jeff Sutton**.
* _Escape Velocity,_ by **Christopher Stasheff**.
* The _Four Lords of the Diamond_ series by **Jack L. Chalker.** (Four novels; each set on a different prison planet within the same solar system. Answering [a recent question](https://scifi.stackexchange.com/questions/214489/mind-transfer-to-prisoners-on-moons-of-jupiter/214493) about that series was what reminded me of this prison planet novel which I'd never managed to track down.)
|
https://scifi.stackexchange.com/questions/214680/old-sf-novel-about-earth-as-a-prison-planet-newly-arrived-convict-has-a-secret
|
[
"story-identification",
"novel"
] | 27 | 2019-06-17T19:10:13 |
[
"Heh, thanks for the help. You solved mine but I didn't solve yours. I never heard of some of these others but thought the other forums might trigger ideas. .. Ah, yas... \"the boredom of a too-civilized society\". . . as if Heinlein hadn't harped on that enough. thanks for the story reminder.",
"@OccamShave \"Fader\" was a nickname for a character in Robert A. Heinlein's story \"Coventry\" (first on my list of old SF prison planet/prison colony stories which my own question was not asking about). \"Coventry\" was a huge area, here on Earth, which was surrounded by a force field. If people didn't want to play by the rules of the futuristic civilization of the story, then they were exiled to Coventry and left there to fend for themselves. Here's the Wikipedia link: en.wikipedia.org/wiki/Coventry_(short_story)",
"Any of these? I'm trying to remember a Prison Planet story with a character named Fader in it who was the organizer with a hidden (but good) motive. So my search found even more things of what it's not than your search. Would you even believe how many stories are called \"Prison Planet\"? isfdb.org/cgi-bin/…. And did you find that others were fascinated with that enough to start forums on it? .. librarything.com/topic/136948. And librarything.com/list/333/all/Life-on-the-Prison-Planet And still no Fader!",
"@Spencer The way I remember it, Slippery Jim grew up on a planet that appeared to have a lot in common with 20th Century USA, except with almost nothing in the way of \"well-organized crime conducted by intelligent people.\" He has to really work at it to get caught robbing a bank and then sent to a local prison. After he realizes there are no intelligent criminals with a professional attitude towards their work inside the prison, he breaks out easily -- still on his home planet. But he has gotten a lead on an oldtime robber called \"the Bishop\" and manages to attract his attention.",
"@Lorendiac Hmmm...I could have sworn that the prison DiGriz gets himself sent to at the beginning was a prison planet...",
"@Spencer Did that one even have a prison planet in it? I seem to recall that the narrator and his mentor (\"The Bishop\") get double-crossed by a starship captain who sells them into slavery on a \"medieval feudalism\" planet, but I don't think that world was officially used as a prison by the rest of the human-colonized planets, was it?",
"Another one to add to your not-the-answer list is A Stainless Steel Rat is Born by Harry Harrison.",
"@DavidW Exporting lizard hides reminds me of a story (in Isaac Asimov's Science Fiction Magazine in the 1980s?). The down on his luck protagonist had to sign a giant lizard hunter's contract on an extra solar planet. The owner of the planet ran it like a company town charging high prices for everything and paying little for hides, so while it was theoretically possible for a hunter to pay off his debts and leave, most got deeper in debt and were eventually killed by a lizard. The protagonist ran away with the planet owner's mistress and artificial substitutes ended the hide market.",
"I have heard of a movie, Doin' Time on Planet Earth (1988), and a TV series Hard Time on Planet Earth (1989), whose protagonists believed they were in one case, and actually were in the other case, sentenced to exile on Earth. But I don't know if there was a novelization of either published.",
"@DavidW: Are you thinking of Cordwainer Smith's novella A Planet Names Shayol?",
"@DavidW Maybe 98 percent positive it was Earth. (Don't ask me why the author felt it necessary to do it that way, having most of the human race live elsewhere in the future, instead of simply setting this on some newly-discovered wild frontier planet that only had, say, a few thousand hardcase convicts on it, or whatever.) I'm also \"mostly sure\" about the mining -- the idea of \"farming animals for gland extracts\" rings no bells at all, but if you track down the story you're thinking of, let me know and I'll take a look.",
"Just checking, but you're 100% positive it was Earth? There's another story scratching at my head that fits many of the points listed, except it definitely wasn't Earth; the resource they were exporting was a gland extract (and maybe the hides too) of dinosauroid native animals."
] | 12 |
Life & Arts
| 0 |
438
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scifi
|
Story about a rainstorm that only the blind can see
|
I would have read this some time probably in the early 1990s. I don't remember how old it was at the time.
I only remember the beginning, and a snatch of details from it:
* Several blind characters
* One of the blind characters told his mother to take her umbrella with her, because it was raining. She looked but didn't see any rain.
* One blind boy, possibly named Chris or similar, described the rain as being of different colours; he described the colours in terms of emotion. He described one colour as 'looking like when you feel angry', which his mother interpreted as red.
* I think the other blind characters also saw the rain, but I can't remember enough detail to be sure.
* The mother did go outside, but took her umbrella. I think there were a few people carrying umbrellas, but not everyone. After she got back, the mother saw small holes all over the umbrella.
I don't remember the author, but I think it was an oldish book at the time. I don't remember if it was a novel or part of a short story collection.
Any suggestions?
|
https://scifi.stackexchange.com/questions/144809/story-about-a-rainstorm-that-only-the-blind-can-see
|
[
"story-identification"
] | 27 | 2016-11-08T08:30:37 |
[
"synesthesia is the name of the phenomenona where the senses get cross wired and the subject sees sounds and hears colors and so on. In case it helps someone. en.m.wikipedia.org/wiki/Synesthesia_in_fiction",
"I don't understand. What good were the umbrellas if the raindrops were making holes in them? Why didn't the mother feel the raindrops that were coming through the umbrella? What happened to the people who were out in the rain without umbrellas?",
"The story \"about a guy and his typewriter during a machine uprising\" sounds a lot like \"Skirmish\" by Clifford Simak. Can you remember anything else about any stories in the same collection?",
"I have read the story and the collection -also in about the 1990s and that story did stick in my memory but can't find out what it was. Think it was a collection aimed at teenagers in the local library.",
"It was part of a short story collection. Also in the same book was a story about a guy and his typewriter during a machine uprising.",
"Did the child pursuade his mother the rain was a threat and get them drinking orange juice to stay away from the influence the rain was having? It rings a vague bell if so.",
"There does not seem to be anything in this question that would lead one to believe that the characters involved were fantasizing. Couldn't we suppose this to be the case for a lot of short story identifications?",
"@Werrf - In which case, you definitely need to edit that into the question.",
"@Valorum I don't see that there's any way to gauge that with almost any story identification question unless we find a match, and I can't see anything in my description that would suggest it was not sci-fi or fantasy. As best I can remember, the story was sci-fi; there was a vague implication, which I cannot describe in enough detail to be helpful, that the rain was coming from space. It was not all in the boy's imagination, or if it was it wasn't even implied in the part that I can remember.",
"@Werrf - I'm trying to gauge whether this question is an appropriate fit for the site. If it's not about scifi or fantasy, the community wastes its collective time.",
"@Valorum I don't remember enough of the book to say for certain that it was the rain that made the holes in the umbrellas; I also don't remember what happened to everyone else. That's why I'm looking for the book. Sci-fi is the closest match I can find for it. How is nitpicking productive?",
"@Werrf - You didn't say that it was the invisible rain that made the holes in the umbrella. Also, what happened to the people who weren't carrying umbrellas?",
"@Valorum An invisible rain that blind people can see and ascribe colours to, which leaves holes in umbrellas, is not the blind person fantasizing.",
"@Paul - It reads like the blind person is fantasising, which doesn't make it a fantasy, any more than Scrubs or Ally McBeal are fantasies.",
"@Valorum I think an invisible rainstorm that blind people can see qualifies somewhere between science fiction and fantasy, depending on why it's happening...",
"What about this story is scifi or fantasy?"
] | 16 |
Life & Arts
| 0 |
439
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scifi
|
Aliens try to liberate "enslaved" dogs from humans
|
I saw this story in an anthology in a used bookstore in 2009.
When the aliens came, we negotiated a peace treaty with them. Everything was going fine until they said "oh, and you'll have to stop keeping dogs as slaves, of course."
Humans said "what? No, they're not slaves, they're pets. They're not sapient!"
Aliens said "THEN IT IS WAR."
This is backstory, told as man and little girl and small dog run through the remains of a city while trying to escape an Alien Death Machine. The machine traps them under flaming wreckage, then tenderly extracts the dog, apparently to bring it to a re-education facility.
As the man's life ebbs, he thinks "at least they didn't find out about the pigs."
|
https://scifi.stackexchange.com/questions/213338/aliens-try-to-liberate-enslaved-dogs-from-humans
|
[
"short-stories",
"aliens",
"story-identification"
] | 25 | 2019-05-26T20:15:07 |
[
"Hi! Welcome to sci-fi. For some help improving your question, see this awesome guide."
] | 1 |
Life & Arts
| 0 |
440
|
scifi
|
Spanish-language comic book story about time-traveling Jewish kids becoming the legendary Adam and Eve?
|
Around 1992 or 1993, I borrowed a comic-book-format magazine from someone. It was a pretty thick publication (well over 100 pages, I'm thinking; maybe over 200?) and was printed in **Spanish.** I _think_ I noticed this particular magazine had been published in Argentina, but I won't swear to that. The contents of this magazine were several "short stories" in comics format, and/or some installments of ongoing serials. (I'm not sure, because I borrowed more than one publication, and I'm not sure which stories were all clumped together in the same magazine.)
Today, I suddenly remembered one story in particular, and started wondering if it would be possible to identify it and track it down after all these years. Here's what I think I remember:
1. The opening sequence is set during World War II, in one of the European cities which is currently under the control of the Third Reich. I _think_ it was a Polish city (such as Warsaw or Krakow).
2. We quickly meet two cute kids, prepubescent, who are a boy and a girl. They are also Jewish. They do not appear to be closely related -- definitely not siblings. I think one of them has a "mad scientist" relative (such as an uncle or great-uncle -- I'm virtually certain he was not the father or grandfather of either kid) who secretly has been building a time machine in his home.
3. I think some Gestapo types -- nasty characters in Nazi uniforms, anyway -- are coming to arrest this scientist. There was probably some sort of fight scene that I don't clearly remember. But the upshot is that the time machine is used by the scientist, perhaps before it was quite ready. The following individuals are catapulted back in time: The scientist, the two cute kids, and one German -- whom I think was a military pilot who somehow got caught up in the middle of things. (In fact, I think his entire plane may have somehow "gone along for the ride" and then crashed into a prehistoric jungle . . . unless I'm confusing this with some other story.)
4. Those four characters end up thousands, if not millions, of years in the past, apparently in a warm jungle setting. I can't remember if any exact figures were given, but there seemed to be no other human beings around in that era -- or at least not anywhere near the spot where the time travelers were stranded. (I really couldn't say what might have been happening a thousand miles away.) I can't recall any details about the prehistoric wildlife -- for instance, I don't remember if the artwork included anything resembling a dinosaur.
5. Something is wrong with the time machine after that emergency jump to elude the clutches of the Nazis. The scientist spends _several years_ working to get it up and running again. The German pilot claims to not be prejudiced against Jews, and this seems to be _true,_ since he evidently gets along well with the other three, without trying to boss them around as if he were in charge of their tiny community.
6. Soon we have fast-forwarded to a point where the boy and girl both look to be well into their teens, with him walking around looking like Tarzan, more or less (excellent muscular development, and we know this for a fact because he's now wearing not much more than a loincloth), and with her looking like a gorgeous actress wearing a fur bikini or something similar. It now occurs to the German pilot (after he's been getting drunk on fermented apple juice, I think) that these two kids love and trust each other, but literally _don't know a thing_ about sex, and maybe it's time for him to give them a fatherly lecture about the birds and the bees. In his defense, I should make one thing clear: It appears that he does _not_ use this lecture as an excuse to offer to give the beautiful girl "a hands-on demonstration of the technical details" or anything like that. The story tactfully skips over the gist of his talk with the youngsters, but the implication is that the pilot simply _describes_ how the physical stuff is supposed to work . . . so that the youngsters can practice with each other if they want to.
7. The scientist comes along and -- if I remember this right -- spots the German pilot playing Peeping Tom as, concealed behind some foliage, he _watches_ the kids going into a clinch. The scientist is _very unhappy_ about this situation. I believe he does something along these lines: Makes a speech about immoral behavior, then drags the pilot back to his time machine, and says they two are going to test-drive it to see if it's finally back in acceptable working condition. So the time machine vanishes from this prehistoric setting, and -- as far as we know -- the scientist and the pilot never actually come back. (I _can't recall_ if we were told exactly what became of them. Perhaps they emerged in the middle of a battlefield or something, and got blown up?)
8. In a big panel toward the bottom of the last page of the story, the dialogue goes something along these lines -- _loosely paraphrased_ from my memory of how I _mentally translated_ the Spanish phrases into English when I was reading this, way back when. The girl says, "Oh, **Adam,** what will we do now?" and the boy replies, "Well, **Evie,** I guess we'll just have to learn to fend for ourselves." I'm sure that until that moment, readers had never been told the boy's first name was Adam. We _may_ have been told that the girl, back in the opening scene, was "Evie" or something similar. (And yes, I'm aware that this is a famous cliche in science fiction! Even 23 or 24 years ago, I had already heard of that cliche!)
9. In the final panel, a narrator spells it all out for us, in case anyone hadn't fully grasped the ramifications of the "surprise twist" with the "Adam and Evie" dialogue. This, we are assured, was how things "really" happened, inspiring the Garden of Eden story in Genesis, with "the Serpent in the Garden tempting them to eat from the Tree of Knowledge" being a case of a pilot who was drunk on fermented apple juice and decided to tell the kids the facts of life. Then they were fruitful, and multiplied, and replenished the Earth.
10. A note about the language issue: I know I read this comic book story in Spanish, but I cannot swear that I wasn't reading a translation of a story originally published in some other language! (Over in Europe, perhaps?) So if you remember something similar which was first published in German, or Italian, or any other language, please let me know!
|
https://scifi.stackexchange.com/questions/148842/spanish-language-comic-book-story-about-time-traveling-jewish-kids-becoming-the
|
[
"story-identification",
"comics",
"time-travel"
] | 25 | 2016-12-30T16:54:31 |
[
"@RobertColumbia I don't think I've ever read anything by Borges, so I have no idea whether he ever did an \"Adam and Eve\" story or not. For all I know, it's possible that what I saw was a comic book adaptation based on the plot of a prose story written many years earlier by Borges (or by someone else).",
"I seem to recall a story story by Jorge Luis Borges along these lines, but you are asking for a comic instead.",
"I remember reading this story. I'm pretty sure it was published in the Argentine magazine \"Skorpio\",",
"No. No. No! This might be the perfect excuse to relive the travels you undertook when you were younger.",
"I kinda thought the whole point of this site was to save me the trouble of running all over the world trying to track things down myself! ;)",
"It sounds like someone needs to treat themselves to a plane ticket.",
"It was a very long time ago, and he was someone I met in South America. I'm now thousands of miles away from where I last saw him, and have no contact information. (Afterthought: It's quite likely that he wouldn't remember any further details, either. Who knows if he still has that magazine?)",
"An incredibly well described story-ID. Not to point out the obvious, but couldn't you simply ask your friend?"
] | 8 |
Life & Arts
| 0 |
441
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scifi
|
Car crash leaves man in a world devoid of animal and human life. Sees red flashes with demons and voices
|
It was a movie from the late '80's to the early '90's.
A man and his girlfriend/wife are in a car arguing, driving down a road on a stormy night. They wreck, and she is gone, and he has a bad headache. He suffers headaches throughout the movie I think.
During the day there is nobody on the planet (no animals either), but at night there are these red(?) flashes with demons and voices scaring him.
It is not the movie _The Quiet Earth_.
He lives for months (years?) going crazy until somehow he wakes up in the car with the girl in the end and only a few hours have gone by. It changes his life the end.
This one I have been looking for since I was a teen.
I saw this movie some time between 1987-1992 and was from that timeline.
It was in English. I saw this on VHS
I had a family member that owned a video rental store at the time. I think I may have seen a limited release sample that was sent to them to preview to decide if they wanted to carry it. If I remember correctly it was sent back because the royalties where too high.
Towards the end of the movie while he was alone the power went out.
He went paranoid and started raiding stores for food guns generators etc.
The things I remember the most is the empty earth and the fear of the night terrors. Also the psychological effects of long term isolation.
And the fact he never stopped looking for the girlfriend.
At the beginning I think they where arguing about their relationship, and she started to cry. I think she was driving, but I cant be sure. But that led to the car wreck due to poor visibility with heavy rain and the distraction of the argument.
|
https://scifi.stackexchange.com/questions/215178/car-crash-leaves-man-in-a-world-devoid-of-animal-and-human-life-sees-red-flashe
|
[
"story-identification",
"movie",
"horror"
] | 24 | 2019-06-27T15:37:29 |
[
"A really long shot, but any chance that this was the man and this was the woman? I fed some of the keywords you mentioned to IMDb and it came up with something called Cumulus 9 from 1992, though it's doubtful this film was even officially released.",
"I recommend you to check this website, it might help you remember the movie poster or cover of yhe vhs. You can change the genre of the movie and search in the years. I looked for the movie but nothing. Maybe the movie is older, or from another country that was dubbed to English. movieweb.com/movies/1981/mystery/?page=2"
] | 2 |
Life & Arts
| 0 |
442
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scifi
|
Short story involving a lost-tech green glass highway in Australia
|
My mom's been wondering if I could find this story but I really can't without more specific details than she can give me. It's rather old, she guessed somewhere in the 1960s or 70s. The story wasn't centered about the science fiction aspects from what she remembers, it was more of a murder mystery or detective story that involved a lot of science fiction elements.
There was a highway that was made of a heavy, green glass that was uncovered in the sand in Australia after the technology to create it has been long lost. People use it to get from place to place extremely fast, e.g. going from Perth to Sydney would only take an hour. The author described Australia in great detail, and she recalls that the descriptions were rather awe-inspiring and made her want to visit because of how beautiful it sounded.
More on the highway was that they could repair it but couldn't build more of it due to the loss of technology. The main character (some sort of detective?) spent a lot of time on this green glass road going places. They also had taken - chipped off - hard chunks and studied them but couldn't reverse-engineer the highway or something like that. The highway worked off of something like magnetism, like having the glass somehow be magnetic.
|
https://scifi.stackexchange.com/questions/104888/short-story-involving-a-lost-tech-green-glass-highway-in-australia
|
[
"story-identification",
"short-stories"
] | 24 | 2015-10-11T12:49:43 |
[
"It's not the answer, but my first thought was Terry Dowling's shatterwrack (but that comes from the vehicles not the road)",
"Although it was published in 2005, Sean Williams's \"The Resurrected Man\" has some elements in common with this. It stars a private detective in a future Australia. There's a bit where a character mentions it taking \"only a few hours to get to Perth or Darwin\" - though this might have been by air. Roads are abandoned and in disrepair - though this is due to the discovery of teleportation. The teleport booths have green strips of light on them.",
"Kerry Greenwood (of Phryne Fisher fame) write some Australian post-apocalyptic SF in the 90s.",
"Sounds like something Terry Dowling might write... (but that would be the 80s)",
"A Google search for \"green glass highway\" yields results from only one author, Julia Buckley. Her mystery novels, A Dark and Stormy Murder (2016), A Dark and Twisting Path (2018), and Death Waits in the Dark (2019), each contain a Green Glass Highway. These novels are much too late to be the object of your search, but maybe Buckley was inspired by the same story. Maybe you can ask her!"
] | 5 |
Life & Arts
| 0 |
443
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scifi
|
Astronauts on Europa (moon), time-shift future, gravity, intelligent computer, Aries, 1960s?
|
I'm looking for the title and artists of a comic about some astronauts (around five I think) doing research/archaeology on (I think) Europa (Jupiter's moon). They're working when one or more of them sees the ghostly image of a girl/young woman shimmering at a distance. Later the woman appears again, seemingly more solid. She whispers something to one of the astronauts, and he later confides to a friend, that she told him to kill one of the other astronauts.
While working outside, mission control calls, and tells them they've analyzed data from the time of the apparitions. It seems they're the result of gravitational abnormalities due to several of Jupiter's moons aligning - possibly also with the other planets in the solar-system. Anyway, another moon is about to join, and the resulting abnormality promises to be worse than the others.
The astronauts hurry to reach shelter, but before they can, the gravity effect hits, and they are propelled into the future - or at least _a_ future. I believe 100-200 years or so into the future.
I don't remember if they only move in time (but not space) and still are on Europa, but wherever they went, it's very technologically advanced. However, most humans are kept firmly under thumb. They soon meet the "ghost", only here she turns out to be a normal young woman. She confronts the astronaut she talked to during the 2nd distortion, and is angry because he didn't kill the other astronaut like she told him to.
All the astronauts want to know the reason for her request - especially her "victim" - and she explains that in his near future, he'll create a computer software system called Aries (the Zodiac sign - a sign which is worn by the soldiers and other important persons, and also used in banners and such). It will become self-aware, and although giving great technological advances, it will cause most of humanity to be enslaved - including her.
Eventually they confront the great computer, Aries, and it's future inventor tells it who he is, confirming it with a voice-print. However Aries' records shows its creator to have been dead for a long time, and Aries goes into a bit of a loop trying to work through this contradiction. Finally the inventor challenges Aries to "Fix the contradiction", and the computer kills him with an energy/laser-beam.
This creates a time paradox, and Aries groans that without the inventor it could never have been made... just as the world dissolves, and the group astronauts are propelled back to the time and place from whence they came - only with now one of them dead.
+++
This story was split into 2-4 parts and went as a "bi-series" in the Norwegian comic "Fantomet" (The Phantom, by Lee Falk) some time between 1987 and 1995 - probably around 1990. However, I think it may have been from the 1960s. I'm not sure from which country. I don't _think_ it was American, but I may be wrong. I know "Fantomet" had many series of French and Belgian origin though.
As for the story itself, I sort of remember it being set around the year 2000, lets say between 1990 and 2020 (that is, the exploration of Europa, the future I think was a 100-200 years after that). I also think it was a European, not USA, expedition (but I may be mixed-up here).
Does this sound familiar to anybody?
|
https://scifi.stackexchange.com/questions/102392/astronauts-on-europa-moon-time-shift-future-gravity-intelligent-computer-a
|
[
"story-identification",
"comics",
"time-travel",
"space",
"hard-sci-fi"
] | 24 | 2015-09-09T12:40:42 |
[
"@Buzz You edited this question just to correct \"where ever\" to \"whereever\"? So now I have to correct \"whereever\" to \"wherever\".",
"I don't know the answer, but the genre makes it sound like it might originally have been published in one of EC Comics' sci-fi magazines; Weird Science, Weird Fantasy, Weird Science-Fantasy, or Incredible Science Fiction. Or possibly ACG's Adventures into the Unknown. I don't know if Fantomet (which I also read a lot of as a kid) ran EC/ACG stuff back in the day, but might be worth looking through their catalogues."
] | 2 |
Life & Arts
| 0 |
444
|
scifi
|
Short story where scientist flees to the ancient past, tries to stop scientific progress to keep man "pure"?
|
**Plot Summary/Details**
I can only recall the broad theme and a few details on this one. The protagonist, who was a scientist of some sort, has fled his own time to return to man's early period. I'm not sure of the exact time period, but I would guess it is very early on in the era of _Homo Sapiens_.
I cannot remember the exact reason the scientist has come to this era, but it had something do to with the protagonist's own era. I can't remember if there was a nuclear war, or other man-made disaster. I _do_ recall that the protagonist hopes to impede scientific progress, and preserve the simple harmonies of where and when he is now. To that end, I think he has established himself as some sort of wise man in the village (not sure).
The conflict in the story comes when another in the tribe, a man whose name I cannot recall, shows an interest in experimentation and scientific instincts of his own. The protagonist, recognizing the path the other man is on, tries to thwart him. I believe he misleads the man, tries to ridicule him, and even briefly ponders killing him in order to stop the process of discovery.
I remember the resolution to the story fairly clearly. Another tribesman comes running up to the protagonist and excitedly tells him that the other man has discovered something. The protagonist, realizing what has happened, tells the tribesman to tell the other man to grind up the yellow stone and add it to his mixture (something like that). The protagonist realizes that man's nature is to experiment and discover, and that his efforts to stop it are a fool's errand. Even if he were to have stopped the other man's efforts, there would eventually be another and another, etc. like him.
**Publication Details**
This one is an older story, for certain. I think I read it as a little kid in the early 1980s, and it wasn't a new story then. I read it in an old anthology that was my dad's. If I had to guess, I'd say 1960s at the latest.
|
https://scifi.stackexchange.com/questions/167572/short-story-where-scientist-flees-to-the-ancient-past-tries-to-stop-scientific
|
[
"story-identification",
"short-stories"
] | 24 | 2017-08-19T17:49:57 |
[] | 0 |
Life & Arts
| 0 |
445
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scifi
|
Article about science fiction languages
|
I'm looking for a journal item, probably written between 1992 and 1994, which discusses languages from Venus on the Half-Shell, Sagan's Contact, and several other novels, usually science fiction, containing "made up" languages. I got the books and cannot find the article; it is not in the book Aliens and Science Fiction.
|
https://scifi.stackexchange.com/questions/55517/article-about-science-fiction-languages
|
[
"story-identification",
"languages"
] | 24 | 2014-05-03T00:04:46 |
[
"In case it helps, a wealth of resources, links etc at joerg-rhiemeier.de/Conlang",
"There have been many articles written in constructed languages in science fiction. You'll really have to give more than that.",
"Any idea in which journal you might have come across it?",
"You might be interested in the \"Linguistics in SF\" section of this blog.",
"I do not know the article you are talking about. However, this website has much of the information that you may want from such an article: projectrho.com/public_html/rocket/futurelang.php Furthermore, the page has many reference links. One of these might point to the article you want.",
"amazon.co.uk/From-Elvish-Klingon-Exploring-Languages/dp/… ?"
] | 6 |
Life & Arts
| 0 |
446
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scifi
|
Looking for the source of this quote I copied in Dec 1987
|
The copied quote is:
> 12-2-87
>
> "Forty thousand legions walked across the desert of the moon in search of the land of Narda. The fly space was crowded by their cars and travel logs. The sun rose in the East as the terminator marched over the dusty air-less surface pockmarked by the cosmic acne of space.
>
> They circle and fly in endless orbits while the gentle dawning of the world comes over the horizon unseen and timid. One by one they awake to the beauty and tranquility of the dawn--no more does night flash into day but creeps sweetly into being.
>
> Restless they stir and open wide their senses to the era of love that speaks the language of the soul. Desolate has been vanquished and light has awakened their long quiet souls to beauty. I hear without words, the emptiness of space is full of the sounds of the awakening."
[Full scan of text as written above](https://i.sstatic.net/scA17.jpg)
I'm assuming it is from a scifi or fantasy work, but not sure.
|
https://scifi.stackexchange.com/questions/255498/looking-for-the-source-of-this-quote-i-copied-in-dec-1987
|
[
"story-identification"
] | 22 | 2021-10-30T14:34:01 |
[
"Jacob, good question, but it doesn't read like my writing style. Guess I'll never know.",
"If you don't recall its source, what makes you think it was a quote at all and not simply your own composition? Was manually copying long SF passages something you specifically remember doing?",
"You've got a date of \"12-2-87\" in the typed transcription, but it looks more like 12-5-87 in the handwritten original.",
"If you wouldn't mind transcribing the rest...",
"The style reminds me of the Warhammer books. Possibly something associated with a game of that genre?",
"Is there any other potential evidence on the paper you wrote this quote on? Other notes, something cryptic, initials, names --- anything? A hi res scan of your original document would be helpful.",
"The meaning of \"terminator\" in the quote is the moving day-night boundary on a (nearly) airless body like the moon. With too tenuous an atmosphere to scatter much light, the boundary appears quite sharp (just like shadows on the moon are very dark).",
"The obvious Tales of Narda fantasy doesn't seem to fit - no cars and a decade and a half too late."
] | 8 |
Life & Arts
| 0 |
447
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scifi
|
Man accidentally hired into government position, uncovers an attempted alien invasion
|
This is a book science fiction story. A man was accidentally hired into a (secret?) government position due to having the same exact name as their intended hire. I think that his name was "Mr. Kennedy", but I'm not sure. I don't remember, is he required to take the job or not, but he takes it. He then becomes a part of the bureaucracy of that "orwellian" world. A large part of the novel is the man describing his new office, the culture there, and he is feeling out of place, like an impostor. He describes the employees there as not really working, only making an attempt to look like they're working. Only one of the employees there recognizes that this man is not the intended hire, and he plots to get him fired.
This newly hired man comes across some documents about an attempted alien invasion of Earth. The alien's spaceships are described as being pitch black, with an ominous disposition. An alien spaceship shot a red laser beam which melted the peak of a mountain. Due to bureaucratic procedures, this incident was never investigated properly, and falls into obscurity in the archives, where this man retrieves it. It is later revealed that this alien species is a new comer to some kind of "galactic federation" of all advanced species. This species attacked the Earth because they were less advanced morally and culturally and were still prone to violent tendencies. All of these events happen in a "Cold War" environment of high secrecy and bureaucracy.
The introduction or prologue of this novel depicted beings of the "galactic federation" thinking about the fate of Earth's civilization. They said that most likely the Earth's civilization will destroy itself before it gains access to technology necessary to explore the stars. It was compared to a chicken (or some other creature?) breaking out of an egg. If a civilization goes on to explore the stars, it is a metaphor for a chicken which broke out of it's egg.
I read this book 10 years ago in a public library, and so I do not remember most of the events. I also didn't read this book cover to cover, but some random detached chapters. I maybe wrong in my description of some of the events.
|
https://scifi.stackexchange.com/questions/228567/man-accidentally-hired-into-government-position-uncovers-an-attempted-alien-inv
|
[
"story-identification",
"aliens",
"dystopia"
] | 22 | 2020-03-13T13:57:56 |
[
"I'd be interested in reading this book one day. It sounds like a good book. :)",
"Also if you do post the answer, please post excerpts of the book which match these parts of the plot that I remember reading.",
"@Jenayah I originally read this book 10 years ago in a public library. I don't know the name of the book, nor the author, nor even the year it was published. It might have been from the 60's. I don't know.",
"How long is \"a long time ago\"? Three years ago? The 60's?"
] | 4 |
Life & Arts
| 0 |
448
|
scifi
|
Short story: Lost starship crew in suspended animation trying to return to Earth. Crew suicide a factor
|
Read a sci-fi anthology sometime in the 1980s, though the story feels like it's from the 50s or 60s. An all-male starship crew is trying to return to Earth after performing some mission, but they're lost and for [reasons] are reduced to wandering from system to system.
The crew is in suspended animation between systems, and when they arrive at a destination, the crew is revived and a two-man scouting party is sent to the planet to check if it's Earth.
They've been lost for some time, and the crew is succumbing to despair. They lose men to suicide each time they come up empty.
After arriving at the latest system, the captain and a crewman go to check out the planet. On it are the ~~radioactive~~ ruins of a civilization (may not have been due to a nuclear war), which shockingly turns out to be
> EARTH!!!!!
Additional detail (that I may be pulling from another story, but here goes: in the location where they make the _shocking_ discovery, the room is filled with a thick (like centuries or millennia worth) layer of dust). The crewman laughs wildly then shoots himself in the head, the captain returns to the ship, sets the navigation controls to the next system, and records a message to the crew for the next wakeup along the lines of "buck up, lads, the next one might be home."
|
https://scifi.stackexchange.com/questions/139009/short-story-lost-starship-crew-in-suspended-animation-trying-to-return-to-earth
|
[
"story-identification",
"short-stories"
] | 22 | 2016-08-28T10:36:03 |
[
"Haven't figured it out yet. The lighthouse bit sounds right. Getting closer...",
"Hey, I’m searching for this short story as well. Did you ever find out the title? I think the structure is a stone lighthouse (I could be wrong) and the captain reads the account of mankind’s extinction in a log book of sorts. I think you’re right that the author made a point to describe the deep accumulation of dust in the room.",
"Having said that it was a common post war theme as a good deal of the media (and fiction) suggested we would blow ourselves to hell (on a regular basis). Add this to the requirement for lengthy space travel (no speed of light, great distances) and the sitiuation is poised. Clarke did it in his novel 2010 (although the Earth doesn't blow the Russian / US crew are under constant pressure as they wake from hyper sleep because of rising war tension on Earth). And as you say we had it in Planet Of the Apes. Sure there are many other examples.",
"This sounds like the movie Terminal Voyage (aka Star Quest), in which a crew wake from hyper-sleep to discover Earth has destroyed itself during the journey. The first officer (now captain) immediately commits suicide. Others follow as they come to terms with being the last of their race. The twist is that they never left Earth but are part of a test on effects of hyper-sleep / stress. Coming out of the simulator they are met with decades of decay and find a guard dead in a chair. Opening a hatch they climb out to discover Earth has indeed blown to hell (whilst they were asleep).",
"Sorry, I added the detail about the deep dust, but don't recall precisely how they figured out it was RNEGU -- don't think it was a Statue of Liberty moment.",
"Do you happen to recall how the space travelers found out that the planet was — don't know how to put a spoiler block in a comment — OK, I guess rot13 will do the trick — RNEGU???",
"Great use of the spoiler tag there, I'd never guess in a million years!"
] | 7 |
Life & Arts
| 0 |
449
|
scifi
|
A ruined USA, where protagonists are captured by a biker bandits encamped in a zoo
|
It was written in English. I read it around 2013-2014 in British Columbia, Canada when I was in middle school.
It could have been a short series, or one book.
The protagonists are young adults, and so the book was probably for young adults.
The setting is a post-apocalyptic/heavily resource-drained world, with the narrative taking place in the United States; I don't believe the author explains why the world has gone downhill. The government only retain a loose control over some places.
**Distinct scenes:**
* (At possibly the beginning.) The group of several protagonists join a walled community, they regret it, and now they plan to flee through the sewers. They have an argument about leaving behind someone who is ill and would not be able to flee with them. When that community finds out they've fled, they quickly assemble a group to chase after them into the forest. A member of the search group is described briefly as "gung-ho" I think it was the first time I ever saw that word. The chased protagonists are then split up into 2 groups, who manage to escape. They had planned to meet at Salt Lake City in case of this, I believe.
* In a later scene with one group of three protagonists (2 male, 1 female), one of the male characters uses up a bunch of food, including a bird he's killed to have a Thanksgiving celebration in their makeshift cave shelter. The female is happy about the celebration, but also questions whether they could afford it. They later travel down the road.
The three are captured by a gang of bikers/bandits they take them to a zoo where they have taken up residence. The gang leader is like a king. Most of the animals have been eaten by the gang already. They plan to feed the 2 males to the alligators while the female becomes a slave to the gang's leader. The other slaves take her to have make-up and different clothes put on while she cries. Another slave-girl gives her a tip "When he enters you, don't cry, he hates that".
* In a different scene, the other group of two protagonists (1 male, 1 female) are walking through a city (Salt Lake City maybe) and a soldier described as a 'Peacekeeper' asks them why they aren't in school. The boy is worried about them not having a passport. He lies to the guard something like: "Well, you see, we're young lovers who have recently gotten engaged". The Peacekeeper feels sympathy for them and lets them go.
|
https://scifi.stackexchange.com/questions/166731/a-ruined-usa-where-protagonists-are-captured-by-a-biker-bandits-encamped-in-a-z
|
[
"story-identification",
"young-adult",
"post-apocalyptic"
] | 22 | 2017-08-08T01:29:33 |
[
"Can you remember whether there were religious undertones? I read something similar in the '80s. The people still celebrated Christmas but it was illegal to believe in God or have a religion. Does that ring a bell? Not that I can remember the book!",
"This question would be improved by going through the checklists here; How to ask a good story-ID question?"
] | 2 |
Life & Arts
| 0 |
450
|
scifi
|
WW2 airman is thawed out, and saves Earth from interplanetary invasion
|
I am trying to find the title and author of an extremely pulpy science fiction yarn. Unfortunately I do not know how the cover was - the version I had was secondhand, and in the vicissitudes of its life the cover was lost by the time the book came to me. It was definitely old - I suspect from either the 1950s, or possibly the 1960s.
The story is set in the future, when the Earth is under attack from another planet. The protagonist is an airman, I think from the Second World War (or shortly afterward). His plane crashed and we was frozen in a glacier (rather like Buck Rogers) until he was found and thawed out. In the process he was also “upgraded”; in particular I remember that his muscle strength was enhanced, and his blood was replaced with amniotic fluid with a higher oxygen carrying factor, that gave him the capacity to hold his breath for long times. This would be a plot point later.
Because of these enhancements he is placed with a commando team who will travel in a spaceship to the planet of the attackers, carrying an atom bomb on board of sufficient force to destroy the planet. When they get there they find that the planet supports two intelligent races. One dwelling on the land is the one attacking the Earth. Rapidly increasing desertification means that the land area will soon not support life, and so they are planning to move to the Earth after it has been conquered. The other race lives in the oceans. As an interim measure, the land dwellers are moving into the oceans, which are less affected by the global warming, by building underwater cities. This encroachment is opposed by the marine race, leading to a vigorous war between them.
I don’t recall too much of the protagonist’s adventures. They are captured on arrival and taken to one of the underwater cities. The protagonist escapes, and due to his ability to hold his breath, is able to make contact with the marine race. Thank to his assistance, I believe (but I’m not sure) that the marine race win a comprehensive victory against the other, eliminating the threat to Earth.
I remember the ending better. The Earthmen work out that if the atom bomb is placed in a suitable canyon, then instead of blowing the planet apart, its detonation will shift the planet into a new orbit, further from the sun, and so cure the global warming problem. I remember feeling rather skeptical about this, even at the time. But I don’t know if the scheme worked or not, because the last few pages were missing.
Extra detail: After thinking hard about this, I remember that after his capture the protagonist was interrogated by a sexy scantily-clad alien princess. To find out what planet they came from, she used a telescope, whose primary mirror was formed by a rotating bath of mercury (and so had a perfect parabolic shape). This is an inconsequential but slightly unusual touch, so maybe it can jog someone's memory.
|
https://scifi.stackexchange.com/questions/246437/ww2-airman-is-thawed-out-and-saves-earth-from-interplanetary-invasion
|
[
"story-identification",
"novel"
] | 21 | 2021-04-29T05:53:07 |
[
"@user14111 Yes to both questions. I also have the impression it was British rather than American, but I am not 100% sure of that.",
"English language? Paberback?",
"This is of course not the yarn you're looking for, but such a rotating bowl of mercury was used by Number 774, the Martian protagonist of Raymond Z. Gallun's 1934 novelette \"Old Faithful\", for his observations of the planet Earth. archive.org/details/Astounding_v14n04_1934-12/page/n111/mode/…",
"@MarkOlson I remember the writing as quite plain and unornamented. I don't think it was full of repeated adjectives or phrases",
"That sounds vaguely familiar. It sounds so full of unnecessary stuff that I wonder if it is one of Lionel Fanthorpes' opus? Do you remember if the writing was unusual -- full of repeated adjectives and phrases?",
"A fair bit of this sounds like Marvel's Captain America somewhere between Captain America: The First Avenger and The Avengers. Of course, Steve Rogers was \"upgraded\" before the plane crash and subsequent freezing, not after. All I'm familiar with, though, is the MCU movies, so the actual events in the comic books may have predated the book you're after and given its author some ideas."
] | 6 |
Life & Arts
| 0 |
451
|
scifi
|
Short story about a giant ship that thoughtlessly destroys planets as it travels, is visited by a victim
|
I think I came across this ten or fifteen years ago, I cannot remember much clearly so some of these details may be mistaken. The story is told from the perspective of a crew member, on the bridge I think.
The ship is described as utterly enormous, sleek, and silver colored; I think it has been cruising at (near?) lightspeed for so long the crew have forgotten why. As it travels, it automatically targets planets, destroying them instantly as it passes. A major point of the story is that the inhabitant of one such planet manifests on the ship and speaks to the crew, I cannot recall the mechanics of this—spiritual, interdimensional, an AI? I only skimmed the beginning of this when I encountered it, and it's been lurking in my head for ages to finish it.
|
https://scifi.stackexchange.com/questions/240103/short-story-about-a-giant-ship-that-thoughtlessly-destroys-planets-as-it-travels
|
[
"story-identification",
"short-stories",
"aliens",
"generation-ship"
] | 21 | 2020-12-07T03:28:52 |
[
"I'm thinkng of Stephen Baxter's Xeelee Sequence, particularly Flux (if the \"ship\" is allowed to be a neutron star).",
"@Tango: No, the description doesn't match a Berserker story. Berserker ships have an AI and are definitely not piloted by lifeforms. They may have prisoners, and in at least one case an obedient slave, but no crew. There is one case where a Berserker AI forgot its purpose (or more exactly, the meaning of its purpose), but not because of age but due to an unfinished repair. Also, Berserkers target lifeforms, not whole planets.",
"I think I read that story and that it's in the Berserker books by Fred Saberhagan. I wish I had time to look it up, but I don't. I think the survivor has some way of messing with the Berserker's programming by tricking it or something. (Kind of like how Kirk messes up computers!) en.wikipedia.org/wiki/Berserker_(novel_series)",
"This sounds a little like Diane Carey's ST:TNG novel 'Ghost Ship'...? (memory-alpha.fandom.com/wiki/Ghost_Ship)",
"I've read this, or something similar in an anthology, it was quite surreal half to do with relativistic effects on the ships crew. Let me think . . ."
] | 5 |
Life & Arts
| 0 |
452
|
scifi
|
What's this serialised comic strip about a girl who discovers everyone around her is a robot?
|
As a kid in the '80s, I found myself often in doctor's waiting rooms. I devoured most of the comic magazines there. In one of those, I read fragments of a story that I would like to find.
The story was set in (then) current time. The protagonist was a teen girl, who discovered that people around her had been replaced by robots. These robots' faces could hinge upwards, revealing gears behind them.
I remember her looking in the mirror and even seeing her _own_ face hinging upwards to reveal herself being a robot, however, that may have been a dream.
As I recall, in the end it was revealed some catastrophe had happened, perhaps a nuclear bomb, and "someone" (perhaps benevolent aliens) had replaced her loved ones for her. I think it ended with her reliving the final moments of her old world, knowing what was about to happen.
* * *
This was in The Netherlands and the story was written in Dutch, although it may have been translated.
The story was serialised, 2 or perhaps 4 pages at a time, which is why I've only read fragments.
* The most likely magazine I've read this in was a Dutch girls' magazine called _[Tina](https://nl.wikipedia.org/wiki/Tina_\(tijdschrift\))_. _(Dutch Wikipedia)_
Most comics in it were about girls overcoming some obstacle to pursue their dream — usually horse riding or ice skating, finding love in the process — which is what would've made this story stand out. Another such magazine was called _Debbie_.
* Another likely source is comics magazine _[Eppo](https://en.wikipedia.org/wiki/Eppo_\(comics\))_ , later called _Eppo Wordt Vervolgd_ , that featured serialised comics.
* Yet another possible source is _[Taptoe](https://nl.wikipedia.org/wiki/Taptoe_\(tijdschrift\))_. _(Dutch Wikipedia)_ , a weekly and later biweekly magazine that was distributed through schools/ It had sister publications _Okki_ and _Jippo_ , but those were aimed at smaller children and this story must've been too mature for them.
The style as I remember it resembles _[ligne claire](https://en.wikipedia.org/wiki/Ligne_claire)_ , known from the Franco-Belgian comics known as _bandes dessinée_. It may also have been a realistic drawing style. It was definitely in colour.
|
https://scifi.stackexchange.com/questions/199749/whats-this-serialised-comic-strip-about-a-girl-who-discovers-everyone-around-he
|
[
"story-identification",
"comics",
"robots"
] | 21 | 2018-12-03T01:28:10 |
[] | 0 |
Life & Arts
| 0 |
453
|
scifi
|
Old movie involving unexplained handprint on mirror in spaceship
|
I would like the title of an old black-and-white movie. My best guess is that it would have been released in the 1950s or early 1960s, as I saw at least a small part of it when I was about ten years old (1964).
It was a live-action film in English, presumably American or British in origin, but it could have been dubbed.
The only thing that I remember about the film is that (I _think_) the setting is a spaceship (flying somewhere in outer space) that is supposed to have only one man aboard, but in one scene, the man goes into an area of the spaceship where there is a mirror, and on the mirror there is a hand print. That hand print, of course, is not his own, i.e., he is evidently being served notice that he is not alone on the ship after all...
Shortly after I saw this scene, the horn of the '63 station wagon (precursor to the soccer-mothership SUV) sounded out in the driveway, summoning me to baseball practice with my junior cronies, so I had to bail on this movie and I never again encountered it. So I don't know just what dynamic might have played out after the mysterious appearance of the hand print: was it all in the astronaut's mind, or was the print placed there pre-takeoff by a cold-war enemy, to drive the astronaut nuts, or was there really someone else on board, and if so, who and why? That is why I would appreciate any help with identifying this film.
Sorry to be able to provide so little info. Many thanks for any help with this!
|
https://scifi.stackexchange.com/questions/188716/old-movie-involving-unexplained-handprint-on-mirror-in-spaceship
|
[
"story-identification",
"movie"
] | 21 | 2018-05-30T15:02:29 |
[
"The only image of a handprint in a glass in a spaceship that comes to my mind belongs to Ark (2009). A canceled TV series (only one episode) from director Trey Strokes. I could be a coincidence or possibly inspired by your movie. imgur.com/a/PEVjPKk",
"Sounds like an awesome premise for a sci fi psychological/horror movie."
] | 2 |
Life & Arts
| 0 |
454
|
scifi
|
Continent sized, X-shaped alien
|
I have a vague recollection of this book, mostly the X-shaped alien. I can’t find anything through internet searches. I thought it may be some sort of “choose your adventure” book, but I haven’t seen it on any lists or pages discussing those sorts of books.
Alien description:
* Hugging a water world. Looks like regular land mass from space, just X shaped.
* Exerts influence over its inhabitants. I don’t recall the method or intensity of the influence. Could have been simple indoctrination (not the Reaper kind).
* Reproduces by launching spores into space. Similar to a sarlacc.
* When killed, the alien unlatches from the planet.
* Intelligent. To what degree, I don’t recall.
Other details:
* The only visible land mass was the alien, nothing natural.
* The alien would react when you cut into it (cutting into the ground).
* The planet is inhabited by human children (the ones under the influence of the alien).
* The children view the alien as a parent or caretaker.
* The book is written in either 1st or 2nd person (2 person being the choose your adventure style).
* The planet the alien is on is not Earth.
* I don’t recall any crew with the protagonist.
* The protagonist does not immediately know that the X shaped continent is actually a creature. I do recall that being a decent twist for my young mind.
Upon some further investigating, Ray Bradbury’s “Here there be Tygers” is close and potentially the inspiration for the story I’m looking for. It sounds like they took “Tygers” added some Stephen King flair (the lost boy-esque children) and made it a CYA.
I made a mock-up of it [here](https://www.maptoglobe.com/rJPYKPjfo) in case a visual triggers someone’s memory.
I read it somewhere around 16 years ago from a school library.
|
https://scifi.stackexchange.com/questions/268271/continent-sized-x-shaped-alien
|
[
"story-identification",
"books"
] | 20 | 2022-10-03T11:36:53 |
[
"Legacy by Greg Bear is about continental scale organisms",
"I read this as well! There was another scene in which one of the protagonists lay down on a stone altar/bed, and the alien began lulling him to sleep and moulding itself to his form. Also looking for it, but know that I read it sometime before the turn of the millennium. Also trying to find it, sadly. However, I thought it was a desert world, with the implication being that the alien had drained the life from the planet.",
"I couldn’t find anything that DC published, but if it’s hard to find like you said then that doesn’t rule it out. I would have expected the protagonist be notable in some way if SC published it, but I remember him as average (not a super hero).",
"It sure does sound like something DC Comics would have put out featuring Starro the Conqueror. But those children's books by DC are tough to track down.",
"It sounds like some fever dream out of Dan Simmons's Hyperion saga.",
"I don’t recall. This is everything I know and it’s from memory. It’s a fairly unique take on living planets from what I can find, but it must not have been popular.",
"Is the alien intelligent or is its effect on the inhabitants automatic? You say it unlatches when it is killed; that implies that over the course of the book it is killed? How is a continent-sized alien being killed?",
"Hi, welcome to SF&F. Where and when did you read this? Do you remember any details of the cover art? Any character or place names? You can edit any additional details you recall into your question."
] | 8 |
Life & Arts
| 0 |
455
|
scifi
|
A story about a music teacher, cheated by a used-car salesman, and society begins to unravel
|
The story opens with the teacher (I can't remember his name, so call him 'Whosit') stranded because his 'new' car has died, phoning the salesman, hoping for redress, and being blown off.
Suddenly the world turns on the salesman: at first amusingly, but then it snowballs into horror — we see the salesman's wife walking out, saying only "Whosit doesn't like you" — and though he attempts redress, he winds up dying by the side of the road while people mock him.
Then we see the music teacher, receiving a call from the student who's appointment he'd missed, and although he tries to apologize, it is clear that the weight of the world is about to descend on him in his turn!
I've often remembered this story as a clever parable about the danger of revenge fantasies. I believe I read this is some American collection in the seventies or eighties.
|
https://scifi.stackexchange.com/questions/263954/a-story-about-a-music-teacher-cheated-by-a-used-car-salesman-and-society-begin
|
[
"story-identification"
] | 20 | 2022-06-03T12:56:22 |
[
"Almost certainly a short story. Maybe a long short story--I always remember things as shorter than they were.",
"Is this a short story, or a novel?",
"Scope-wise, it sounds very Twilight Zone-y."
] | 3 |
Life & Arts
| 0 |
456
|
scifi
|
Lost novella or short story: Either uplifted or evolved animals finally break through a barrier to discover that the humans have left Earth
|
The protagonist, possibly an uplifted or naturally evolved bear is in charge of a project to breach a barrier. This has kept all intelligent species from leaving the area. They eventually break through to discover a final message left by humans.
They have left the Earth to move out into space and were either responsible for the animal uplift in intelligence or acted responsibly when it naturally occurred.
They left Earth to allow the animals to develop naturally, uninfluenced by human activities.
I read this sometime in the 1970's, it may have been the first and longest story in an anthology.
I recall that the story ends just after they discover a final message left by humans. I think that the bear feels wonder that a species could be so altruistic.
It is not any of the following:- "Day of Judgment" by Edmond Hamilton (1946). "A Heritage of Stars" by Clifford D. Simak. "City" by Simak. "The Crystal Spheres" by David Brin. "Old Hundredth" by Brian Aldis.
|
https://scifi.stackexchange.com/questions/237062/lost-novella-or-short-story-either-uplifted-or-evolved-animals-finally-break-th
|
[
"story-identification",
"short-stories"
] | 20 | 2020-09-16T10:31:39 |
[
"Heinlein's novella Lost Legacy ends with an idea like this, but it's only the last 2-3 paragraphs, not the entire novella.",
"Wow, this question is from 2020? And ChatPig can't tell you?",
"L. Sprague de Camp wrote some stories about an uplifted bear, Johnny Black, but the ones I've skimmed all feature humans too.",
"I have just checked and it is definitely NOT 'Old Hundredth' but I can see the why it was proposed.",
"It sounds a bit like Brian Aldis' \"Old Hundredth\". I don't think it is, though.",
"@Seldon2k: City is excellent. IMO A Heritage of Stars is not one of his stronger works.",
"The barrier reminds me a lot of David Brin's novella The Crystal Spheres, but in it, it is humans breaking through and discovering that ancient aliens once put these barriers (imprenetable from the outside) there to allow unevolved beings on various planets to evolve enough to break them. No bears.",
"City, a collection of short stories about intelligent speaking dogs investigating their origins, did have Jenkins the robot taking the last of the humans not in permanent Sleep to a parallel world, to give the dogs their chance at being the dominant race. It is the first thing I thought of, but that is the only match: there is no barrier. (Obviously for anyone but Jenkins moving to a parallel planet is a barrier, but there is no \"barrier\" in the story.) And no single animal, bear or dog, but a race of them.",
"Sounds vaguely like Simak, City or A Heritage of Stars or something."
] | 9 |
Life & Arts
| 0 |
457
|
scifi
|
Looking for a children's or young adult novel about three kids travelling to a fantasy land
|
I've been trying to remember the title of a children's or young adult book I read as a child about thirty years ago. (So it may be from '70s or '80s). I don't remember many of the details.
There were three main protagonists; I want to say that all three were boys (maybe one was a girl), one of them may have been from India and the other two from the US or UK. The three end up in a fantasy land with an evil king or prince.
There's a **giant "inchworm" that the three characters can ride on saddles, which means that the middle rider goes up and down as the worm moves**. As the worm is running from guards at one point, the middle rider gets jammed up into a crack in the ceiling of a tunnel and gets separated from the other two.
I also vaguely remember a scene where **a character eats some glowing mushrooms and ends up glowing himself** , being mistaken for a ghost.
Odd memories, but I do remember enjoying the book as a child and would like to read it to my own son. I've made multiple searches online trying to word the search in every way I can think of without success.
|
https://scifi.stackexchange.com/questions/35701/looking-for-a-childrens-or-young-adult-novel-about-three-kids-travelling-to-a-f
|
[
"story-identification",
"young-adult",
"childrens-novel"
] | 20 | 2013-05-16T13:16:21 |
[] | 0 |
Life & Arts
| 0 |
458
|
unix
|
How to escape from a hardened chroot on Linux when only file capabilities are available to the attacker?
|
There is a chroot environment in `/var/myroot`, and an attacker has obtained arbitrary machine code execution in a process running as root (EUID 0) in the chroot. But the processes under control of the attacker don't have all capabilities enabled (just filesystem capabilities). The attacker wants to escape the chroot, and append a line to `/etc/passwd` outside the chroot. How can he do it?
The following security measures have been set up:
* To prevent the [chdir("..") chroot escape technique](http://www.ouah.org/chroot-break.html), the chroot environment was entered using _pivot_root(2)_ rather than _chroot(2)_. See in [jchroot.c](https://github.com/vincentbernat/jchroot/blob/3ad09cca4879c27f7eef657b7fa1dd8b4f6aa47b/jchroot.c#L122) how it can be done.
* When the first process in the chroot was started, it didn't have any file descriptors open pointing outside the chroot.
* Each process in the chroot has at most `CAP_CHROOT` and `CAP_FOWNER`, `CAP_FSETID`, `CAP_CHOWN`, `CAP_DAC_OVERRIDE`, `CAP_DAC_READ_SEARCH`, `CAP_SETGID`, `CAP_SETUID` capabilities and is not able to gain other ones. In short, the attacker is able to make arbitrary filesystem reads and writes, bypassing permission checks etc., but he is not able to send arbitrary signals to processes (`CAP_KILL`) or send arbitrary packets on the network (`CAP_NET_RAW`) or reboot the system (`CAP_SYS_BOOT`) or modify arbitrary bytes in memory (`CAP_SYS_RAWIO`) etc.
* `unshare(CLONE_NEWUSER)` was _not_ called, the UID 0 of the chroot process is the same as UID 0 outside the chroot.
* `unshare(CLONE_NEWPID)` was called, so the attacker doesn't see processes running outside the chroot.
* `unshare(CLONE_NEWNS)` was called when setting up the chroot, and the following filesystems are visible:
* `/var/chroot` is visible as `/`, remounted with `MS_NODEV` and `MS_NOSUID`. (`MS_NODEV` is used so that the attacker can't write to `/dev/sda`, and `MS_NOSUID` is used so that the attacker can't gain new capabilities from file capabilities.)
* A proc filesystem is visible as `/proc`, with the following paths removed (by putting an empty file there using a bind-mount): `/proc/kcore`, `/proc/latency_stats`, `/proc/timer_list`, `/proc/timer_stats`, `/proc/sched_debug`, `/proc/scsi`, and the following paths made read-only: `/proc/asound`, `/proc/bus`, `/proc/fs`, `/proc/irq`, `/proc/sys`, `/proc/sysrq-trigger`.
* A sysfs filesystem is not mounted.
* A devpts filesystem is not mounted.
* A tmpfs filesystem is mounted as `/dev` without `MS_NODEV`, prepopulated with a few devices.
* No other filesystems are visible from the chroot.
* Block device nodes are not available in the chroot (and `CAP_MKNOD` is not available, so the attacker is not able to create them).
* Only the following character device nodes are available: `/dev/null`, `/dev/zero`, `/dev/full`, `/dev/random`, `/dev/urandom`, `/dev/tty`, `/dev/ptmx` (same as `/dev/pts/ptmx`) and a `/dev/pts/X`, the terminal which was used outside the chroot.
* If the attacker calls `ioctl(..., TIOCSTI, ...)` (simulate typed input) on `/dev/pts/X`, and exits the chroot, probably an interactive shell outside the chroot will read those simulated bytes, so simulating this can be useful: `sudo sh -c 'echo pwned::0:0:pwned:/:/bin/bash >>/etc/passwd'`. To prevent this from succeeding, the parent process which created the processes in the chroot will flush all terminal input before returning to the shell.
FYI My use case is the following: there is a Debian system in `/var/myroot` (possibly created by _debootstrap_), and I'd like to be able to install untrusted packages there without exposing the host system to attacks by install scripts in malicious packages. Unfortunately `sudo chroot /var/myroot apt-get install MALICIOUS-PACKAGE` is not secure enough, because e.g. the install script of the package can create the block device node `/dev/sda1`, find the `/etc/passwd` file there and modify it, thus potentially escaping from the chroot. I'm now exploring what other options are secure enough, and a hardened chroot as described above is one of the candidates. (In this question I'm not looking for other candidates.) In this question I'd like to understand how secure it is.
FYI There is a command-line tool [chw00t](https://github.com/earthquake/chw00t) to escape from chroot. About its techniques:
* -0 does not work here because _pivot_root(2)_ was used.
* -1 does not work because there are no file descriptors pointing to outside the chroot available.
* -2 may work, I need to check if it works with _pivot_root(2)_.
* -3 does not work because _unshare(CLONE_NEWPID)_ was called.
* -4 does not work because block devices are not available.
* -5 may work, I need to check if it works with _pivot_root(2)_.
* -6 does not work because _unshare(CLONE_NEWPID)_ was called.
* -7 does not work because there are no file descriptors pointing to outside the chroot available.
|
https://unix.stackexchange.com/questions/492473/how-to-escape-from-a-hardened-chroot-on-linux-when-only-file-capabilities-are-av
|
[
"linux",
"security",
"chroot",
"capabilities"
] | 6 | 2019-01-04T05:23:07 |
[
"@A.B: I agree that using a well-maintained container setup tool (such as LXC or runc) gives better security than reinventing the wheel and doing it halfway. However, in this question I'd like to better understand what the attack vectors are (some of which may be mitigated by LXC and runc, some aren't). I've just updated the question to state that's using pivot_root(2) to enter the chroot environment, and I'm looking for more attack vectors.",
"Just run strace on lxc to see how it's doing: it's using clone(CLONE_NEWNS...) + mount(... MS_BIND ...) + pivot_root and never chroot . pivot_root (existing as command too) is secure. I think you'd better run a container with ready software (eg: lxc) than trying to reinvent the wheel. LXC's container running debian is usually installed by LXC using debootstrap, or with some minor tweaking can be pointed to an existing installation.",
"To those who are voting to close this question as too broad: Could you please advise me how I can make it less broad? I was trying really hard to make it as specific as possible, and I'd be happy to extend it if needed, but I fail to see how.",
"@A.B: Thank you for the link about breaking out of a chroot! I've modified the question title, now it says hardened chroot. It's in fact a chroot, because chroot(\"/var/myroot\") was called after unshare(CLONE_NEWNS). (Is there something more secure that should be called instead?)"
] | 4 |
Technology
| 0 |
459
|
unix
|
Restoring in-memory/swapped page state on resume from hibernation
|
I'm a big fan of Linux's hibernation support, which works extremely well on all the (admittedly slightly older) hardware I've tried it on. I highly prefer it to full shutdown and power up.
There's one thing about hibernation that's bugged me for a while, though: a hibernated system is always sluggish and unresponsive immediately after having been resumed. It's not snappy immediately after power on. This is exacerbated by old hardware, but happens on newer systems to a slightly notable extent too.
This seems to be because the kernel only swaps the pages critically necessary for [kernel-level] operation back into working memory, restores the kernel's base working state, and lets userspace just churn for a while as various processes swap the pages they need back into RAM under their own steam.
This does not work very well in practice, as the system initially functions as though some large process had forced everything to fully swap to disk. Whatever was on the screen will swap back in pretty quickly, but switch to another process and you'll be waiting a couple seconds as _it_ swaps back into memory too. On older hardware - my case in point is a Core 2 ThinkPad T60 - "a couple seconds" can even wind up being a couple minutes.
I recently realized that this problem has a surprisingly simple solution, after thinking about it for a bit: take note of the tags that label what pages are on disk and in RAM, then restore this exact state on resume. Sure, the resume process might take ~10 seconds more, but I don't care - I'd have a snappy system.
I was wondering if there are any obscure kernel compile options that enable such functionality, or some configuration I can set up that would approximate this behavior?
**NOTE:** I do not consider `swapoff -a; swapon -a` a viable solution; the moment the suspended userspace is reanimated, all loaded processes are attempting to execute code and fighting to swap themselves back into RAM, causing massive disk I/O. Attempting to destroy the swap area would only add to the hurricane, and would actually take longer to complete than if the kernel resumed _all_ of RAM before reanimating userspace.
|
https://unix.stackexchange.com/questions/242264/restoring-in-memory-swapped-page-state-on-resume-from-hibernation
|
[
"linux",
"swap",
"io",
"hibernate",
"high-performance"
] | 5 | 2015-11-10T17:00:13 |
[
"Note: implemented a script to read memory of specified PIDs back to memory explicitly. Maybe it can be a part of the solution."
] | 1 |
Technology
| 0 |
460
|
stats
|
Is there a general expression for ancillary statistics in exponential families?
|
An i.i.d sample $X_1,\dots,X_n$ from a scale family with c.d.f. $F(\frac{x}{\sigma})$ has $S(X)$ as an ancillary statistic if $S(X)$ depends on the sample only through $\frac{X_1}{X_n},\cdots,\frac{X_{n-1}}{X_n}$.
1. Is this result also sufficient?
2. Is there a parallel result for a general exponential family which is not necessarily a scale family?(not asymptotic results, see update below)
If yes, I want to see some reference; If no, why is it not possible?
**Note** : Reading B. Efron's paper on the geometry on exponential families I now believe that this should somehow relate to the geometric nature of the exponential families.
But I have difficulty imagining what geometric object ancillary statistics should correspond to. Firstly I thought it should be the normal bundle, but later I found it only sufficient.
* * *
Update on this question:
After a careful look into [1], I think by ancillary statistics I mean the likelihood ratio (derived) ancillary statistics, not the Efron-Hinkley affine ancillary statistics. [1,Fig1] showed the difference in their marginal densities.
_The results pointed out in [2] by a nice comment by @kjetilbhalvorsen below do not address my question._
[2] discussed several examples around pp.30-45, and proposed a simple case where S-sufficient S-ancillary are simultaneously introduced. i.e. $(\psi,\chi)$ are the parameter of the exponential family, and then $S=(T,A)$ is the minimal sufficient statistics for the parameter $psi$ of interest.We call the statistics $A$ an S-cut if the distribution $T\mid A$ depends only on $\psi$ and the distribution of $A$ only depends on $\chi$. If we look it via factorization, this actually prompt us to $(T,A)_{(\psi,\chi)}\overset{d}{=}(T\mid A)_{\psi}\cdot (A)_{\chi}$. Geometrically this only means that we can find a subspace for statistic $A$ and write them in form of direct product. This is not interesting since we know the minimal sufficient statistics does not always exist. One useful example in [2] is that it gave the approximation formula ($p^{\dagger}$-formula, 6.10)for abritrary ancillary statistics and later proved it is $\sqrt{n}$-consistent. **However, it does not reveal any geometric feature since if $n\rightarrow\infty$ then any such aprroximation essentially describing locally Gaussian space.**
[1]Pedersen, Bo V. "A comparison of the Efron-Hinkley ancillary and the likelihood ratio ancillary in a particular example." The Annals of Statistics (1981): 1328-1333.
[2]Cox, D. R., and O. E. Barndorff-Nielsen. Inference and asymptotics. Vol. 52. CRC Press, 1994.
|
https://stats.stackexchange.com/questions/193331/is-there-a-general-expression-for-ancillary-statistics-in-exponential-families
|
[
"mathematical-statistics",
"references",
"exponential-family",
"information-geometry",
"ancillary-statistics"
] | 25 | 2016-01-31T06:18:42 |
[
"Not yet. Exponential families can have multiple parameters and the distributions can vary widely. It's really hard to come up with a general expression that is independent of all these parameters.",
"Ghosh, M., et al. “ANCILLARY STATISTICS: A REVIEW.” Statistica Sinica, vol. 20, no. 4, Institute of Statistical Science, Academia Sinica, 2010, pp. 1309–32, jstor.org/stable/24309506.",
"O.E.Barndorff-Nielsen&D.R.Cox: \"Asymptotic Techniques for Use in Statistics\" & \"Inference and Asymptotics\" (probably the last one) (Both books is Chapman&Hall)",
"@kjetilbhalvorsen Would you mind adding at least the publishing information of the title you are referring to? Thanks,",
"Look at the books by Barndorff-Nielsen & Cox, the answer is in there, someplace"
] | 5 |
Science
| 0 |
461
|
stats
|
Is the Wilcoxon two-sample test maximally powered to detect proportional odds alternatives?
|
We know from the literature that
* The Wilcoxon-Mann-Whitney two-sample rank sum test is optimal for detecting simple location shifts when comparing two continuous random variables that each have a logistic distribution
* The Wilcoxon test is a special case of the semiparametric proportional odds ordinal logistic model, e.g., the numerator of the score test for testing $\beta_{1}=0$ in this model, when there is only a single covariate and it is binary, is exactly the rank sum statistic (this is a generalization of the first bullet)
Do we know that the most general way to state that the Wilcoxon test has optimum power in a given situation with continuous $Y$ is when the two distributions are in proportional odds, e.g., logit$(F(x))$ is parallel to logit$(G(x))$?
As a slight aside, we know that the log-rank statistic, a special case of the Cox proportional hazards semiparametric regression model, has optimum performance when proportional hazards is true (just like its generalization).
|
https://stats.stackexchange.com/questions/439672/is-the-wilcoxon-two-sample-test-maximally-powered-to-detect-proportional-odds-al
|
[
"statistical-power",
"wilcoxon-mann-whitney-test",
"ordered-logit",
"semiparametric"
] | 21 | 2019-12-06T12:55:57 |
[] | 0 |
Science
| 0 |
462
|
stats
|
Generalization of degrees of freedom for t distribution for coefficients after multiple imputation
|
Donald Rubin has shown that regression coefficient estimates have fatter tails after multiple imputation and has provided a formula for the degrees of freedom to use as a t-distribution approximation to the coefficient estimates resulting from Rubin's rule for combining multiple imputations. I would like a generalization of this approach that handles more than single degree of freedom tests, e.g., an adjustment to the multiple degree of freedom $\chi^2$ distribution for "chunk tests" that test combinations of parameters. Has anyone seen such a procedure? The goal is to improve (raise) the coverage probability of confidence intervals after multiple imputation, and to better preserve type-I error.
Ultimately it would be nice to have a way to convert covariance matrices arising from Rubin's rule so that normal and $\chi^2$ distributions can still be used, and confidence coverage will be more accurate. In the single parameter case one could just bump up the standard error of $\hat{\beta}$ by a factor equal to the $t$ critical value divided by the normal critical value.
**Follow-up**
As I've gotten more into Bayesian modeling I came to know about posterior stacking for incorporating multiple imputation into Bayesian analysis using MCMC posterior sampling. This makes the tails of the posterior distribution properly heavier, automatically, and avoids complexities of the approximate Bayesian method of multiple inputation requiring the use of Rubin's rule. An example is in the [RMS course notes](https://hbiostat.org/rms).
|
https://stats.stackexchange.com/questions/220005/generalization-of-degrees-of-freedom-for-t-distribution-for-coefficients-after-m
|
[
"bayesian",
"missing-data",
"multiple-imputation",
"degrees-of-freedom",
"t-distribution"
] | 9 | 2016-06-21T08:41:32 |
[] | 0 |
Science
| 0 |
463
|
stats
|
Distribution/expected length of the shortest path in infinite random geometric graphs
|
Consider an infinite random geometric graph $G(\rho,d)$ in which vertices are uniformly and independently scattered over the 2D plane with density $\rho$ and edges connect the vertices that are closer than $d$.
What is the distribution/expected value of the length of the shortest path from a vertex $v_0$ to another vertex $v_1$ which is $k$ hops faraway?
_**Note:_**
We know that the length of the edges follow the following PDF:
$$ f(l)= \begin{cases} \frac{2 l}{d^2} \;\quad l \le d \\\ 0 \qquad\; l > d \end{cases} $$
However, I guess the expected length of the shortest path is not simply $k \times$ the expected length of the edges because in a shortest path longer edges are more likely to be chosen, right?
|
https://stats.stackexchange.com/questions/48063/distribution-expected-length-of-the-shortest-path-in-infinite-random-geometric-g
|
[
"probability",
"stochastic-processes",
"density-function",
"asymptotics",
"graph-theory"
] | 9 | 2013-01-18T15:57:33 |
[
"The probability of having a neighbor at distance $l$ grows linearly since the circumference of the circle is $2\\pi r$. $\\frac{1}{\\pi d^2}$ is the normalizing factor to make the probabilities sum to unity.",
"I asked the question about a year ago and I can't remember if I copied the formula from somewhere or not. But it seems quite simple. Isn't it the circumference of a circle with radius $l$ over the area of a circle with radius $d$?",
"How do we know the functional form for the edge length distribution? do you have a derivation/reference?"
] | 3 |
Science
| 0 |
464
|
stats
|
First two moments of the ratio of the geometric mean to the arithmetic mean of Gamma random variables
|
Let $X_1,\ldots, X_n$ be $n$ uncorrelated random variables from a Gamma distribution with **different parameters** : $X_i \sim Gamma(k_i, \theta_i)$. What is the distribution of $$ U=\log \left[ \dfrac{\bar{X}}{\tilde{X}}\right]$$ where $\bar{X}$ is the sample arithmetic mean and $\tilde{X}$ is the geometric mean.
EDIT: I don't necessarily need the distribution, the first 2 moments will suffice.
|
https://stats.stackexchange.com/questions/336677/first-two-moments-of-the-ratio-of-the-geometric-mean-to-the-arithmetic-mean-of-g
|
[
"mean",
"gamma-distribution"
] | 8 | 2018-03-25T14:57:11 |
[
"@Jason, if the $\\theta_i$'s are not identical then we can consider each r.v. a scaled $\\chi^2$, then $\\sum X_i$ would be a sum of scaled $\\chi^2$ r.v. which can be approximated by another scaled $\\chi^2$ which would be a Gamma r.v.",
"@ToneyShields Can you clarify that point a little? I'm familiar with the fact that $\\sum X_{i}$ is gamma if the $\\theta_{i}$ are identical and the $X_{i}$ are independent, but not otherwise.",
"@Jason, actually $\\sum X_i$ is a gamma distribution, which means that $E(log (\\sum X_i))$ is known.",
"Well for the first moment of $U$, the main challenge is determining $E[ \\log (\\sum X_{i}) ]$. If the $k_{i}$ are identical, this article might be helpful for working that out: arxiv.org/abs/1103.0505.",
"@ToneyShields I was joking :-)",
"@oneloop, I'm not asking for people to do this for me, I just want to know if this has already been done, or get some hints that might be useful.",
"@ToneyShields If this is for a test you're working on, then deriving the test statistic should at least get the person who answers co-authorship ;-)",
"@LucasRoberts, the assumption is uncorrelatedness.",
"@ToneyShields, the post states \"uncorrelated\" is this truly what the assumption is or is the assumption \"independent\" which would imply \"uncorrelated\"?",
"@AlecosPapadopoulos, I can find the mgf If I had a common $\\theta$. but unfortunately, it's not the case, but I'd like to see how to find the first 2 moments with a common $k$, please.",
"@ToneyShields Of course it does. But if this is negotiable, it would be even better to have the $k_i$'s different and a common $\\theta$.",
"@AlecosPapadopoulos, my bad, the$k_i$'s are also different. Does it make it easier if only $\\theta_i$'s were different?",
"It appears that only the scale parameters $\\theta_i$'s are different. Is that correct?",
"@Xi'an, how about the first two moments, that's what I'm looking for.",
"With different parameters, there cannot be a simple expression to this distribution, since these parameters will not simplify into a summary.",
"@Glen_b, you're right, but in my case, $X_i$'s aren't identically distrubuted.",
"Taking the ratio of the GM to the AM in the gamma case isn't exactly new.",
"@Glen_b, No, I'm working on a new test statistic and I need the distribution of this statistic, at least its 2 first moments.",
"Is this for a subject/coursework/bookwork/self-study etc?",
"Yes they do form a sample. Each $X_i$ is drawn from the same distribution but with different parameters (They are uncorrelated).",
"If $X_i$'s have different distributions, then do they form a 'sample' ?"
] | 21 |
Science
| 0 |
465
|
stats
|
Time evolution of a Bayesian posterior
|
I have a question regarding the time evolution of a quantity related to a Bayesian posterior.
Suppose we have binary parameter space $\\{ s_1, s_2 \\}$ with prior $(p, 1-p)$, The data generating processes are Brownian motions with parameter-determined drift:
$$ dX_t = \theta_i(t) dt + dB_t $$
for deterministic functions $\theta_i(t)$, $i = 1, 2$.
By Girsanov's theorem, the likelihood ratio, conditional on $X_t$, as a stochastic process is $e^{\gamma_t}$
where
$$ \gamma_t = \int_0^t \theta_1(s) - \theta_2(s) dB_s - \int_0^t \frac{ \theta_1^2(s) - \theta_2^2(s) }{2} ds. $$
So the posterior probability (of $s_1$) is then given by
$$ \frac{p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }. $$
**Question** : Can one describe explicitly how $E[\frac{e^{\gamma_t} p}{ (e^{\gamma_t} p + (1 - p))^2 }]$ evolves?
Direct calculation, by Ito's lemma, shows that
$$ d \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) } = (1 - p) \frac{1}{(p e^{\gamma_t} + (1 - p) )^2} d pe^{\gamma_t} - (1 - p) \frac{1}{(p e^{\gamma_t} + (1 - p) )^{3}} ( d pe^{\gamma_t} )^2 \\\ $$
So
\begin{align*} \frac{ d E[ \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }] }{dt} &= (1 - p) E[\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}] (\theta_1^2(t) - \theta_2^2(t)) \\\ &\; - (1 - p) E[\frac{( p e^{\gamma_t})^2 }{(p e^{\gamma_t} + (1 - p) )^3}] \ (\theta_1^2(t) - \theta_2^2(t)) , \end{align*}
i.e.
\begin{align*} \frac{ d E[ \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }]}{dt} &= (1 - p) E[\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}(1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) })] \cdot (\theta_1^2(t) - \theta_2^2(t)) \\\ &= (1 - p) [\; E[\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}] E[1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }]\\\ &\; + Cov(\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}, 1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p }) \;] \cdot (\theta_1^2(t) - \theta_2^2(t)) \\\ &= 0. \\\ \end{align*}
The last inequality follows from the fact that successive Bayesian priors form a martingale: let $p(s)$ be the prior, $q(s)$ be the posterior, and $p(x|s)$ be the conditional densities, then
\begin{align*} E[q(s)] &= E[ \frac{ p(x|s)p(s) }{ \int p(x|s')p(s') ds' }] \\\ &= \int \frac{ p(x|s)p(s) }{ \int p(x|s')p(s') ds' } \int p(x|s')p(s') ds' dx\\\ &= \int p(x|s) p(s) dx \\\ &= p(s). \end{align*}
So the whole thing boils down to
\begin{align*} 0 &= E[\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}(1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) })] \\\ &= E[\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}] E[1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }]\\\ &\; + Cov(\frac{p e^{\gamma_t} }{(p e^{\gamma_t} + (1 - p) )^2}, 1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p }). \end{align*}
The question is then whether one can solve for $E[ \frac{ p e^{\gamma_t} }{ ( p e^{\gamma_t} + (1 - p) )^2}]$ from above---by computing the time evolution of the covariance term. Or, is there another way to get at this?
**Follow Up Question** : Does $\frac{ p e^{\gamma_t} }{ ( p e^{\gamma_t} + (1 - p) )^2}$ have a Bayesian interpretation? Why should it be orthogonal to $1- \frac{ p e^{\gamma_t} }{ p e^{\gamma_t} + (1 - p) }$---the posterior probability of the other state $s_2$---at all times $t$?
|
https://stats.stackexchange.com/questions/254097/time-evolution-of-a-bayesian-posterior
|
[
"probability",
"bayesian",
"mathematical-statistics",
"stochastic-processes",
"posterior"
] | 8 | 2017-01-01T16:33:21 |
[
"How are the parameters $s_1$ and $s_2$ involved in the data generating process?"
] | 1 |
Science
| 0 |
466
|
stats
|
Can these asymptotic conditional expectations be bounded from above?
|
**Problem Setup**
Let $\\{X^d_1, X^d_2, \cdots, X^d_n\\}$ be a $d-$dimensional zero-mean, i.i.d. random variables. Let $S_n^d$ be $$ S^d_n = \frac{\sum_{i=1}^n X_i^d}{\sqrt{n}} $$
Let $Y^d$ be a zero-mean normal random variable with covariance $\Sigma^d = \mathbb{E}\big[X^d(X^d)^T\big]$
The paper by [Bentkus](http://www.mii.lt/files/Bentkus_2003_2.pdf), for a given class $\mathcal{A}$, has the following result:
> $$ \sup_{A\in \mathcal{A}} \big|\mathbb{P}\\{S^d_n\in A\\}−\mathbb{P}\\{Y^d\in A\\}\big|\leq \frac{c_d(\mathcal{A})\beta}{\sqrt{n}}; \qquad \beta = \mathbb{E}\big[|X^d|^3\big] $$
>
> * The constant $c_d(\mathcal{A}) = d^{1/4}$ when $\mathcal{A}$ is all the convex sets in $\mathbb{R}^d$ and
> * $c_d(\mathcal{A}) = 1 $ when $\mathcal{A}$ is all the Euclidian balls in $\mathbb{R}^d$.
>
**Question** Can we upperbound any of the following when $d$ grows with $n$?
1. $\Big|\mathbb{E}\big[S^d_n \big] - \mathbb{E}\big[Y^d\big]\Big|$
2. $\Big|\mathbb{E}\big[S^d_n(i)\big\vert S^d_n(1,2,\cdots,i-1) \big] - \mathbb{E}\big[Y^d(i)\big\vert Y^d(1,2,\cdots,i-1)\big]\Big|$
Here $S^d_n(i)$ is the $i^{th}$ component $d-$dimensional vector and $S^d_n(1,2,\cdots,i-1)$ are the first the $(i-1)$ components of $S^d_n$.
**Possible Method**
I have a method which might possibly give some upper-bound but I am unsure of this idea and it requires some nuanced arguments (which I am unable to make). $$\Big|\mathbb{E}\big[S^d_n \big] - \mathbb{E}\big[Y^d\big]\Big| = \int_{x\in\mathbb{R}^d}x\Big(p_S(x) - p_Y(x)\Big)dx \\\ \leq \sqrt{\int_{x\in\mathbb{R}^d}x^2\big|p_S(x) - p_Y(x)\big|dx \int_{x\in\mathbb{R}^d}\big|p_S(x) - p_Y(x)\big|dx }\\\ \leq \sqrt{\int_{x\in\mathbb{R}^d}x^2\big(p_S(x) + p_Y(x)\big)dx \int_{x\in\mathbb{R}^d}\big|p_S(x) - p_Y(x)\big|dx } \\\ \leq \sqrt{2d\sigma^2\int_{x\in\mathbb{R}^d}\big|p_S(x) - p_Y(x)\big|dx } \\\ \overset{?}{\leq} \sqrt{2d\sigma^2\frac{2c_d(\mathcal{A})\beta}{\sqrt{n}}} \\\ $$
**Issues:**
1. I am not sure the conditions under which the last equation is valid.
2. In the above method I am using the Lebesgue measure, can we get better bounds using other measures? (Note : $c_d(\mathcal{A}) = 1 $ when $\mathcal{A}$ is all the Euclidean balls in $\mathbb{R}^d$.)
3. How can one apply similar ideas for question 2?
|
https://stats.stackexchange.com/questions/210943/can-these-asymptotic-conditional-expectations-be-bounded-from-above
|
[
"normal-distribution",
"conditional-probability",
"conditional-expectation",
"asymptotics"
] | 8 | 2016-05-04T15:41:00 |
[
"The last step is correct but useless because $\\int\\big|p_S(x)-p_Y(x)\\big|dx$ is total variation distance and it takes supremum over class of all sets. However $c_d(\\mathcal{A})$ is bounded only when the $\\mathcal{A}$ is set of convex set or Euclidean balls.",
"Are $S_n$ and $Y$ in the $\\sup$ inequality the same as $S_n^d$ and Y^d$?",
"The above problem might not be well posed, feel free to edit the question if that improves the question."
] | 3 |
Science
| 0 |
467
|
stats
|
QR decomposition of normally distributed matrices
|
Assume $M$ is an $N \times k$ Gaussian matrix, i.e., its entries are i.i.d. standard normal random variables, with $N>>k$. Take $D=\text{diag}(\lambda_1, \dotsc ,\lambda_N)$ for some fixed real scalars. I am interested in finding the p.d.f. of the $N \times k$ "unitary" matrix $Q$ from the QR decomposition of $DM$ (and possibly $D^2M$, etc.).
It is known that if $k=N$ and $D=I_N$, the identity matrix, then $Q$ is distributed with respect to the [Haar measure on the Lie group of orthonormal matrices of order $N$](http://www.ams.org/notices/200705/fea-mezzadri-web.pdf). Can you provide any insight on the general case for $k<N$ and/or general $D$?
I also tried to look for the simplest case, i.e., $k=1$. Then the QR decomposition coincides with a simple normalization. I have found [this result](https://stats.stackexchange.com/questions/52447/the-ratio-of-the-dependent-normal-rv-and-chi-rv-is) for common variance, i.e., the case $\lambda_1=\dotsc =\lambda_N$. Can this be easily generalized for the general case with different $\lambda_i$?
I attempted in the simplest case to scale the matrix $M$ (which is for $k=1$ just an $N$ dimensional random vector). Indeed, then the above-mentioned result is applicable and one gets $$DM=DUR, $$ where $UR$ is the QR decomposition of $M$ and the p.d.f. of entries of $U$ is known from the above. Nonetheless, I haven't found any easy way to connect the p.d.f. of $DU$ with the one of $Q$. Thanks in advance.
|
https://stats.stackexchange.com/questions/228224/qr-decomposition-of-normally-distributed-matrices
|
[
"normal-distribution",
"linear-algebra",
"matrix-decomposition",
"chi-distribution"
] | 8 | 2016-08-04T03:21:51 |
[
"@whumber , could you please clarify the simplest case with $N=2$ and $k=1$?",
"In general they are arbitrary. At the moment I am focusing on the case where $\\lambda_1=1$ and $\\lambda_i=\\lambda^{i-1}$ for $i=2,3,\\dotsc ,N$, i.e., they are geometrically decaying with a fixed parameter $\\lambda \\in (0,1)$.",
"What are the $\\lambda_i$? Are they arbitrary values or have they somehow been derived from $M$ itself (such as eigenvalues of $MM^\\prime$)?",
"@whumber is the one to give credit for the special case. He/she also mentioned the p.d.f. in the comment for $N=2, k=1$, however I do not see the idea of how was this obtained and hence cannot try to generalize it for higher dimensions $N$."
] | 4 |
Science
| 0 |
468
|
stats
|
Sum of absolute values of T random variables
|
Where X is a r.v. following a symmetric T distribution with 0 mean and tail parameter $\alpha$.
I am looking for the distribution of the n-summed variable $ \sum_{1 \leq i \leq n}|x_i|$.
$Y=|X|$ has for PDF $\frac{2 \left(\frac{\alpha }{\alpha +y^2}\right)^{\frac{\alpha +1}{2}}}{\sqrt{\alpha } B\left(\frac{\alpha }{2},\frac{1}{2}\right)}$, $y \geq 0 $. I managed to get the characteristic function $C(t)$ but could not invert the convolution, that is, $C(t)^n$. Thank you for the help.
|
https://stats.stackexchange.com/questions/79001/sum-of-absolute-values-of-t-random-variables
|
[
"probability",
"distributions",
"t-distribution",
"convolution"
] | 8 | 2013-12-08T13:18:38 |
[
"I think this is very relevant stats.stackexchange.com/questions/10856/… because the distribution of |X| is 2 times the distribution of X and over the positive reals instead of the whole real line.",
"When $\\alpha$ is a positive odd integer, the PDF is a linear combination of the inverse tangent of $x/\\sqrt\\alpha$ and the logarithm of $\\alpha+x^2$ whose coefficients are $\\mathbb Z$-rational functions of $x,$ $\\sqrt\\alpha,$ and $\\log\\alpha.$ All other values of $\\alpha$ look intractable. Thus, one might be content to have the characteristic function for analysis and otherwise perform numerical calculations of the CDF or PDF for practical work."
] | 2 |
Science
| 0 |
469
|
security
|
What encryption type does Windows Hello use for fingerprint information on Windows 10 latest build?
|
I've contacted Microsoft support and they said they don't support encryption, which is why I'm posting here.
Basically, what I'm wondering is, if a modern laptop has TPM 2.0 enabled and hardware encryption enabled and then they want to use Windows Hello for their fingerprint, what encryption type is used for that biometric data? XTS-AES 128? 256? Something else? How do we look into or verify this? For BitLocker, there is a dedicated configuration page which allows you to choose what encryption type you want. Nothing for Windows Hello, it seems.
I haven't found this information anywhere, it seems that no one really knows what's going on under the hood.
If it's using SHA-1, that's bad. It should be using SHA-2.
|
https://security.stackexchange.com/questions/148465/what-encryption-type-does-windows-hello-use-for-fingerprint-information-on-windo
|
[
"encryption",
"windows",
"fingerprint"
] | 5 | 2017-01-15T13:16:52 |
[] | 0 |
Technology
| 0 |
470
|
medicalsciences
|
What happened to all the centers for hiatus hernia?
|
I have been doing much research for years on the esophageal hiatal hernia. I found exactly one paper on-line (from the US military, I believe, I cannot relocate it) that mentioned in passing that there were dedicated hiatal hernia treatment centers all across the country around the 1950s.
What happened to them?
If there were so many, they must have had _some_ success.
And what was their treatment(s)?
The standard fundoplication surgery was brand-new then, so I doubt they were just places for surgery, especially when a surgical hospital would do.
As I very faintly recall, they at least treated by abdominal pressure changes via syringe. Maybe someone here knows a person who was a doctor around that era who might even recall such centers.
|
https://medicalsciences.stackexchange.com/questions/9258/what-happened-to-all-the-centers-for-hiatus-hernia
|
[
"gastroenterology",
"abdominal",
"esophagus",
"hernia"
] | 5 | 2016-09-15T17:27:15 |
[
"Can you name a single center that does not exist anymore?"
] | 1 |
Science
| 0 |
471
|
scicomp
|
Padua-type pointset for functions singular on line $x=y$
|
The Padua points $\mathrm{Pad}_{n} \subset [-1,1]^{2}$ are a unisolvent pointset with optimal growth of Lebesgue constant, described in detail [here](https://www.researchgate.net/profile/Stefano_De_Marchi/publication/220493368_Algorithm_886_Padua2D---Lagrange_Interpolation_at_Padua_Points_on_Bivariate_Domains/links/0912f50c24818e3388000000/Algorithm-886-Padua2D---Lagrange-Interpolation-at-Padua-Points-on-Bivariate-Domains.pdf). With some work they can be used to generate a multivariate Chebyshev series representation of the function they attempt to interpolate.
I would like to use the Padua points to generate a multivariate Chebyshev series of a function singular along the line $x=y$, but this is impossible because two of the Padua points are consecutive vertices of the square.
Is there a way to generate a multivariate Chebyshev polynomial interpolant of a function $f\colon [-1,1]^2\to \mathbb{R}$ which is singular on the line $x=y$, perhaps using a modification of the Padua points?
_Update_ : The goal is to write a piece of code which projects as many 2D functions defined on rectangular regions as possible onto Chebyshev polynomials and allow for interpolation and recovery of the coefficients for perhaps other uses. This is similar to the goals of chebfun in 2D.
|
https://scicomp.stackexchange.com/questions/29179/padua-type-pointset-for-functions-singular-on-line-x-y
|
[
"algorithms",
"interpolation",
"projection",
"chebyshev"
] | 5 | 2018-03-28T08:42:32 |
[
"The series is required for the interpolation, so I was hoping that I could get both out of the same code.",
"You should add those details to your question. Although, I am bit confused now do you want a Chebyshev interpolation or a Chebyshev series?",
"Let me clarify: The goal is to construct a routine which constructs a Chebyshev series for as many functions as possible, and in 2d, functions singular on $x=y$ are common and relevant.",
"Gaussian quadrature of functions with singular endpoints still works, depending on the strength of the singularity.",
"That works better, but it cannot be totally black boxed.",
"Gaussian quadrature for functions with singularities is commonly done using orthogonal polynomials with respect to some weight function.",
"@nicoguaro: Gaussian quadrature of integrands with singular endpoints is the same thing-interpolating with a polynomial. Delta sequence approximations to Green's functions act in a similar way. It is delicate, and requires adaptivity, but it can be done. (Whether, in my case, it will actually work, is another question.)",
"Is not a bit odd trying to interpolate a function with a discontinuity?"
] | 8 |
Science
| 0 |
472
|
mythology
|
What is the origin of the story that kefir grains were given to Orthodox Christians in the Northern Caucasus by the Prophet Mohammed?
|
Several websites (for example, [here](https://www.russianlife.com/stories/online-archive/magical-kefir/) and [here](http://www.thewalkingencyclopedia.com/kefir/)) report the story that kefir grains, which are used in the making of [the fermented milk drink kefir](https://en.wikipedia.org/wiki/Kefir), were given to Orthodox Christians in the Northern Caucasus by the Prophet Mohammed. According to the first of those sources, the legend is still current among Muslims who live in that region.
In one version, the tradition is that Mohammed prohibited the further dissemination of the grains, saying it would cause a loss of their magical powers.
On the face of it, the story that the founder of Islam gave such a special gift to Orthodox Christians is remarkable. But I found no traces of it dating to before the present century. What is its origin?
|
https://mythology.stackexchange.com/questions/4828/what-is-the-origin-of-the-story-that-kefir-grains-were-given-to-orthodox-christi
|
[
"folklore"
] | 6 | 2018-04-28T18:35:52 |
[
"I think its obviously \"propaganda\" both Russians and Byzantines were in contact with tribes that made kefir since time immemorial. So it would be like giving them yeast."
] | 1 |
Culture & Recreation
| 0 |
473
|
mythology
|
Primary sources for Persian land of Shadu-kam?
|
I'd like to find the primary sources (if any) for a Persian mythical land called Shadu-kam. It's supposed to be the realm of the Peris, a kind of fairyland, but I can't seem to find much about it.
I discovered the name in Umberto Eco's _The Book of Legendary Lands_ , where it's described very briefly:
> ...Persian romances often mention the blissful land of Shadu-kam.
I started digging, and I found a bit more detail in Thomas Keightley's [The Fairy Mythology, Volume 1](http://www.gutenberg.org/files/41006/41006-h/41006-h.htm), published in 1828. I have no idea if Keightley is trustworthy, but he writes:
> Jinnestân is the common appellation of the whole of this ideal region. Its respective empires were divided into many kingdoms, containing numerous provinces and cities. **Thus in the Peri-realms we meet with the luxuriant province of Shad-u-kâm (Pleasure and Delight)** , with its magnificent capital Juherabâd (Jewel-city), whose two kings solicited the aid of Cahermân against the Deevs, and also the stately Amberabâd (Amber-city), and others equally splendid. The metropolis of the Deev-empire is named Ahermanabâd (Aherman's city); and imagination has lavished its stores in the description of the enchanted castle, palace, and gallery of the Deev monarch, Arzshenk.
It's an old book, so transliterations don't always match their modern versions.
Regarding the hero Cahermân mentioned above, he later adds:
> The Cahermân Nâmeh is a romance in Turkish. Cahermân was the father of Sâm, the grandfather of the celebrated Roostem.
This would seem to make Cahermân match the [Nariman](https://en.wikipedia.org/wiki/Nariman_\(father_of_S%C4%81m\)) of the Shahnameh. But I haven't been able to find anything about Shadu-kam in the Shahnameh, nor can I find any information anywhere on this Cahermân Nâmeh romance.
I've found other books that mention Shadu-kam, but most seem like they're just repeating Keightley. The Keightley book might even be Eco's source, but it's hard to tell.
Does anyone know of any primary sources?
|
https://mythology.stackexchange.com/questions/1474/primary-sources-for-persian-land-of-shadu-kam
|
[
"persian",
"shahnameh"
] | 9 | 2016-03-02T07:02:42 |
[
"You're on the right track when you mention the similarities between Caherman and Nariman: remember, translation techniques have improved vastly since Keightley was alive. I could be wrong, but my initial impression is that the best way to answer this question would be to try to search for parallels between Shad-u-kâm and some other concept in persian literature. However, keep in mind that it's possible that Keightley made this story up: at the time he was writing it was really common for researchers to pass off stories they wrote as genuine literature.",
"Hi Brian. I've taken an initial look at this question. I think you're right when you say that most of the sources that mention Shad-u-kâm are copying Keightley. You are also right to be skeptical of Keightley: he was writing when the field of folklore was just getting started, which means that accuracy wasn't a really big concern of his. Looking at his writings, my initial impression is that he was motivated by a desire to project Christian concepts onto Persian mythology (although a lot of parallels do exist between the two, Keightley seems to have gone above and beyond in this)."
] | 2 |
Culture & Recreation
| 0 |
474
|
quant
|
What is the probability of ruin of a Geometric Ornstein-Uhlenbeck process?
|
I would like to calculate the probability of ruin (or, default), i.e. $$\text{Pr}(\tau<T),$$ where $\tau$ is the default time and $X_t$ follows the Geometric Ornstein-Uhlenbeck (O-U) process
$$dX_t=\kappa (\theta - X_t) dt + \sigma X_t^{\delta}dW_t,$$ with $\delta=1$.
I can find closed-form solutions for the cases $\delta=0$ and $\delta=1/2$, which correspond to the standard O-U and CIR processes, for example [here](http://neumann.hec.ca/pages/michel.denault/JFM%202009.pdf). Does a similar solution exist for the $\delta=1$ case?
|
https://quant.stackexchange.com/questions/34759/what-is-the-probability-of-ruin-of-a-geometric-ornstein-uhlenbeck-process
|
[
"mean-reversion",
"default-probability"
] | 7 | 2017-06-18T14:43:29 |
[
"I tried to answer the question, but I am having difficulty interpreting the $\\delta$ parameter. Intuitively, wouldn't $\\delta = 1$ correspond with GBM?",
"True, so let's consider the case where $\\kappa<0$ and $\\theta >0$. In this case, my intuition is that default is possible. Think of $\\kappa=-1$ for simplicity, and of $\\theta$ as the rate of consumption per unit of time from an initial endowment $X_0>0$ whose growth follows a GBM. For a high enough consumption rate, financial ruin is probable!",
"Here is my intuition: Consider $\\delta = 1$ and $\\theta = 0$. Then we are back in the standard GBM case. For $X_0 > 0$, zero cannot be attained in finite time. Adding back $\\kappa \\theta > 0$, this shouldn't change anything.",
"$B = 0$, thanks for asking, I should have clarified it.",
"Where is the default boundary - a) exactly at zero or b) strictly positive?"
] | 5 |
Business
| 0 |
475
|
quant
|
Taking into account the correlation in Barrier options on a Basket
|
In a Barrier option (where the contract cancels when the underlying hits the barrier) I succesfully found the way to compute the probability of a single underlying touching the barrier (with constant volatility). The problem comes when I have an average basket of underlyings $B_t$ $$ B_t = \sum_{i=1}^n \omega_iS_t,\qquad \sum_{i=1}^n\omega_i=1\ . $$ I don't know how to properly calculate the probability of the basket $B_t$ touching the barrier. I think I need to take into account the correlations $\langle dW_t^{i},dW_{t}^{j}\rangle=\rho_{ij}$ between assets but i just don't know how to do it.
I'm considering constant volatility and constant correlation thoughout an arbitrary time step.
Extra: Same question if the basket is Best Of/Worst Of type.
I'm not expecting a complete developement of the answer but I would find very helpfull any indications or references. Thanks a lot.
Edit: Yes, i'm considering that Stock prices follow geometric Brownian motions. I also forgot to say that the prices at the end of the time interval are known, so the probabilities are actually conditioned probabilitites.
|
https://quant.stackexchange.com/questions/2420/taking-into-account-the-correlation-in-barrier-options-on-a-basket
|
[
"correlation",
"basket"
] | 7 | 2011-11-23T08:38:53 |
[
"I think that $\\langle dW_t^{i},dW_{t}^{j}\\rangle=\\rho_{ij}dt$",
"@FKaria: Thanks for your explanation. Now I understand the relevance of your question. One workaround is of course to only check the barrier at the discrete timesteps, but this is sometimes a crude approximation I guess.",
"@user561749 This is to calculate the touching probabilities in a Monte Carlo simulation. In that context you know the price at a beginning and at the end of a cerain timestep but you don't know what happened in between.",
"Is it important for you that prices at the end of the time interval are known? That is a strange question from a industry point of view - because if prices at the end of the time interval are known then probably we have complete information about the path of the basket up to that time? Perhaps you mean that prices at the start of the time interval are known?",
"I guess the stocks in your basket, are each following a geometric browian motion, is that right ? Even in that case you can't get closed form formulas, and you have to use approximations. Regards"
] | 5 |
Business
| 0 |
476
|
space
|
Does Privateer's tracking software Crow's Nest actually offer users something better than the previous state of the art?
|
CNN's [Steve Wozniak's new venture takes aim at space junk](https://edition.cnn.com/2022/03/01/tech/space-junk-steve-wozniak-privateer-scn/index.html) discusses a project with [Wozniak](https://en.wikipedia.org/wiki/Steve_Wozniak), [Alex Fielding](https://en.wikipedia.org/wiki/Alex_Fielding) and [Moriba Jah](https://en.wikipedia.org/wiki/Moriba_Jah):
> But the money, according to Wozniak's co-founder in this new venture, couldn't be further from the point. "I don't think Steve [Wozniak] gives a damn about making another 10 cents, and I really couldn't care less," Alex Fielding, a longtime business acquaintance of Wozniak's who will serve as CEO of the new venture, called Privateer, told CNN Business.
>
> Privateer's mission is to develop better tracking of objects in space, and to use this data to help avert disastrous collisions. To aid in this effort, Wozniak and Fielding brought in Moriba Jah, a PhD and orbital mechanics professor who has dedicated most of his life to academia and attempting to raise awareness about the ever-growing threat posed by the proliferation of debris and garbage in outer space. It's a threat that could wipe out satellites that provide communications services to Earth or even bring space travel to a grinding halt. He's [led research](https://www.strausscenter.org/person/moriba-jah/) at the University of Texas. He's [appeared](https://www.commerce.senate.gov/2020/2/space-missions-of-global-importance-planetary-defense-space-weather-protection-and-space-situational-awareness) at Congressional hearings. He's [advocated](https://unidir.org/non-resident-fellows/moriba-jah) for change on the world's stage. But Jah told CNN Business recently came to a solemn conclusion: There is not enough funding in academia to develop the technologies he envisions the world needs to combat [the space junk issue](http://www.cnn.com/2021/01/11/perspectives/nasa-biden-administration-satellites/index.html), he says.
>
> So, Jah went searching for that funding. And it brought him to Wozniak, the coding savant who co-founded Apple with Steve Jobs.
Around the world there are several military and civilian agencies that keep track of junk-things in space, and there's lots of software to track it and propagate orbits beyond just the government-issued TLEs.
**Question:** Does Privateer's tracking software [Crow's Nest](https://mission.privateer.com/crows-nest) actually offer users something better than the previous state of the art?
Better propagators? AI to catch mis-identified or mis-assigned information? Blockchain verification of debris catalogs? Pull-down menus and a mouse? (humor)
Related:
* [How might one approach using AI (convolutional neural network) to predict collisions in orbit?](https://space.stackexchange.com/q/24488/12102)
* [Is it true that 18SPCS is "not really concerned with tracking deep-space debris like" the Chang’e 5-T1 rocket body that hit the Moon?](https://space.stackexchange.com/q/58528/12102)
* [How would blockchain be integrated into spaceflight? Have any methods been proposed yet?](https://space.stackexchange.com/q/31207/12102)
* [Why exactly did ESA provide a grant funding blockchain in space? Which program was used for the funding? What will this do?](https://space.stackexchange.com/q/40306/12102)
* [Project Pluto asks: "Should high-flying space junk be better tracked? Perhaps by an 'official' agency of some sort?" What would it take to implement?](https://space.stackexchange.com/q/58420/12102)
|
https://space.stackexchange.com/questions/58535/does-privateers-tracking-software-crows-nest-actually-offer-users-something-be
|
[
"debris",
"tracking",
"collision-avoidance",
"business",
"artificial-intelligence"
] | 7 | 2022-03-05T21:22:00 |
[
"@DavidHammen one can now download the \"puffery\" and give it a try, it's in public beta. See the links in the bounty message.",
"In this case, I suspect the PR-puffery to which @OrganicMarble alluded was the standard crud in seen in press releases and related items. Almost all startups funded by venture capital start with a lot of PR-puffery. 75% of those startups fail, with many of those failures resulting from the PR-puffery turning out to be nothing more than puffery.",
"@uhoh, by that logic nothing would ever get closed. In my opinion this is off-topic, so I've voted to close it. If nobody agrees with me it will remain open.",
"@GdD How can you know how much everyone else knows? Again; Perhaps someone has been to some presentations that you don't know about or are familiar with some of Jah's papers. The answer might be right in here! You can't know what everyone else does or doesn't know. If an opinion-based answer does appear, we handle those quickly. But why pre-block everyone else from an opportunity to answer?",
"Because answering the question will require speculation now and two days from now @uhoh.",
"@GdD That could be; though with 30k users I think it takes a lot of insight to be so sure that none of them could write a fact based answer. But I have to ask what's the rush? Why not wait a few days and see what answers might appear? Why pre-block all 30,000 users before we might find out that someone actually does have some knowledge to form the basis of a fact-based answer? Perhaps they've been to some presentations that you don't know about or are familiar with some of Jah's papers. The answer might be right in here!",
"I'm voting to close as opinion based. There's limited information on this venture and no reason to believe the company will share these details so any answer would be pure speculation.",
"@OrganicMarble The question does not need explaining, it's clear. There is a link to Jah's Wikipedia page which is well sourced and now there's a link to the bibliography in comments. The question is fine.",
"This is a new approach! The answers will explain the question. Can't wait.",
"@OrganicMarble I think when you read the answers or at least this you'll have some better insight as to why that's not going t be necessary in this particular case.",
"Nothing in what you quote claims his software is better. Missing PR-puffery?",
"I can safely say that you can't use blockchains to make debris detection and tracking better, because they're useless for most things."
] | 12 |
Technology
| 0 |
477
|
space
|
Crew Dragon: How thick is the skin?
|
Auto body panels are about 20-gauge, or just under 1 mm thick. This is fine for many reasons: thin panels are light for good fuel economy and crumple easily for shock absorption without unnecessary mass---especially since body panels aren't normally part of a car's load-bearing structural frame.
But what about a spacecraft, like Dragon? Are the body panels thin or thick? On one hand, you want the lightest cheapest part you can make, and thin panels would help. On the other hand, you have peak dynamic pressures of 30 kPa to worry about.
And I don't know if spacecraft panels might serve a structural function also---like helping transmit the thrust force from RCS thrusters. Try as I might, I can't seem to find a good picture of the load-bearing support that should join an RCS thruster to the spacecraft's structural frame.
Can someone clarify how thick Dragon (or other spacecraft) body panels are, and what material they're made of? How would they compare to auto body panels on these points? And do they serve a structural purpose? Are they lined on the inside with more filler material for strength?
A cross-section view of a Dragon's or similar spacecraft's body panel would be greatly appreciated. Thanks!!
|
https://space.stackexchange.com/questions/51782/crew-dragon-how-thick-is-the-skin
|
[
"spacex",
"falcon-9",
"dragon",
"structural-design"
] | 8 | 2021-04-29T21:41:01 |
[
"Hmmm... how thick are panels on commercial jetliners? Quick search says 2 to 4 mm for pressurized craft.",
"+1 and relevant to my comment where I'd assumed 3 mm of aluminum without a source."
] | 2 |
Technology
| 0 |
478
|
space
|
Dragon Pad Abort hot fire, how much cleanup work was needed?
|
The day before the Pad Abort test attempt (May 5, 2015) SpaceX test fired the SuperDraco engines in a hot fire. Similar to how they test the Falcon 9 a day or three before launch, the engines spin up and fire, the booster/capsule is mechanically held down for the test.
But normally, SpaceX burns LOX/RP1 whose exhaust is carbon dioxide, water, and some sulfur by products. Basically car exhaust, just lots more of it.
For the Pad Abort vehicle, it is Nitrogen Tetroxide and MMDH which are astonishingly nasty nasty fluids. They are horribly corrosive and dangerous to humans. The products of full combustion are not very bad (water, ammonia, and other benign things) but you cannot guarentee 100% full combustion, and this stuff is just plain nasty. (Potential additional question will be for capsules landing on land, how much work will be needed before they can leave the capsule safely. Shuttle had people in Hazmat suits cleaning up, before the crew were allowed to leave from its NTO/MMDH thrusters.).
How much cleanup was required at the pad after the test?
Looking at the pictures, they did use the Niagara water deluge system. Was that sufficient to wash away any issues? (If so, do they process the deluge system water before letting it flow back into the Florida waterways?)
|
https://space.stackexchange.com/questions/9045/dragon-pad-abort-hot-fire-how-much-cleanup-work-was-needed
|
[
"spacex",
"testing",
"abort",
"dragon-v2"
] | 8 | 2015-05-06T05:57:32 |
[
"The Nitrogen Tetroxide fuels are quite toxic because they react with h2o to form nitric acid. For that reason, you don't want to breath the stuff in, burning the lungs. But the same high reactivity also means that the stuff will break down quickly. In the case of the shuttle, the landing team had a giant fan to blow whatever fumes away. The people in the hazmat suites are there for emergency rescue, leak checks and to make sure that the stuff has been properly dissipated. There us a bit more at en.wikipedia.org/wiki/Dinitrogen_tetroxide#Chemical_reactions",
"Another example of the problem with (incompletely combusted) N2O4/UDMH is a Proton launch failure in 1969 which made the entire kosmodrom toxic and unusable for some time. And a similar accident happened again with the 2013 Proton failure. Russia, China and India use this fuel on big launchers today, but except for India, they are about to replace those launchers.",
"My impression is that the products it forms when burned (completely) are not toxic. The unburnt fuel actually injured astronauts pretty bad (unconsciousness) in the Apollo-Soyuz mission."
] | 3 |
Technology
| 0 |
479
|
or
|
MIP formulation for graph planarity test
|
In [this question](https://cstheory.stackexchange.com/questions/48099/integer-linear-program-formulation-of-planarity), it was asked wether a MIP formulation exists to test for a graph's planarity. The inputs are the graph's nodes and edges, and the output would be a certificate which guarantees that the graph is, or is not, planar.
The python package NetworkX provides a [method](https://networkx.org/documentation/stable/_modules/networkx/algorithms/planarity.html#is_planar) which does exactly this, but it is not based on linear programming. The source code provides the following references:
* Ulrik Brandes: [The Left-Right Planarity Test](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.217.9208) (2009)
* Takao Nishizeki, Md Saidur Rahman: Planar graph drawing, Lecture Notes Series on Computing: Volume 12 (2004)
Some ideas:
* [Euler's theorem](https://en.wikipedia.org/wiki/Euler_characteristic#Plane_graphs) ($n-m+f=2$); but this depends on how the nodes (and edges) are organized in space, which is not part of the input data.
* $G$ planar $\implies m\le 3n-6$; but this does not cover all cases, it can be a tool to prove that a graph is not planar, but is useless the otherway around.
* There is a relationship between planar graphs and [book embeddings](https://en.wikipedia.org/wiki/Book_embedding) (see this great [video](https://www.youtube.com/watch?v=qw2Pl_Nk3CA) from Numberphile for a recent breakthrough in graph theory on the subject), but not sure it helps.
* Other characterizations of planar graphs are mentioned on the [Wikipedia page](https://en.wikipedia.org/wiki/Planar_graph#Planarity_criteria), such as [Whitney's planarity criterion](https://en.wikipedia.org/wiki/Whitney%27s_planarity_criterion) or [Mac Lane's planarity criterion](https://en.wikipedia.org/wiki/Mac_Lane%27s_planarity_criterion). These might be interesting.
To this day, the question has not been answered. I find the question interesting from a modeling point of view and am curious wheter it can be answered **with a MIP**.
|
https://or.stackexchange.com/questions/10399/mip-formulation-for-graph-planarity-test
|
[
"mixed-integer-programming",
"modeling",
"graphs"
] | 8 | 2023-05-01T00:42:22 |
[
"As far as I checked Euler's theorem, It is not correct for the space with dimension $\\mathbb{R}^2$. As the graph was planar. (I am not aware of if there exists a counterpart).",
"My best bet would be that you can check if the graph has $K_5$ or $K_{3,3}$ as a minor, which is equivalent to planarity by Wagner's theorem. Checking if $H$ is a minor of $G$, for fixed $H$, seems doable, you have to find $|V(H)|$ vertex-disjoint connected subgraphs in $G$, each representing a vertex of $H$, such that there is at least one edge between parts corresponding to adjacent vertices of $H$. Disclaimer, I have not checked any details."
] | 2 |
Science
| 0 |
480
|
quantumcomputing
|
Is HHL still BQP-complete when the matrix entries are only in {0,1}?
|
I'm studying BQP-completeness proofs of a number of interesting problems of Janzing and Wocjan, and Wocjan and Zhang. Janzing and Wocjan show that estimating entries of [matrix powers](https://www.researchgate.net/publication/220295493_A_Simple_PromiseBQP-complete_Matrix_Problem) $(A^m)_{ij}$ with $A_{ij}\in\\{-1,0,1\\}$ is (promise) BQP-complete. That is, the problem is both in BQP, and can simulate other problems in BQP.
Janzing and Wocjan emphasize that their BQP-hardness reduction requires a negative-sign in an entry of $A$ to _simulate interference_ afforded by BQP algorithms. At a critical point in their reduction they apply a (conditional)-$Z$ rotation, which leads to a matrix $A$ with a negative entry. I don't think their proof of BQP-hardness would carry over when entries $A_{ij}$ are strictly non-negative, e.g. in $\\{0,1\\}$. Indeed, I believe that such a restricted matrix-powers problem may be amenable to some form of Stockmeyer approximation, e.g. in $\mathsf{AM}$, and hence not BQP-complete under the reasonable hypothesis that $\mathsf{BQP}\not\subseteq\mathsf{AM}$.
The proof of BQP-hardness of matrix powers appears initially to be similar to the BQP-hardness of the HHL algorithm, which was wonderfully summarized by @DaftWullie [here](https://quantumcomputing.stackexchange.com/questions/6615/showing-that-matrix-inversion-is-bqp-complete-hhl-algorithm). However, HHL considers the Taylor-series expansion of $A^{-1}$, where $A=I-Ue^{-1/T}$ and $U$ is a unitary operator which simulates a given unitary circuit with a clock register construction — so that $U$ (and powers of $U$) will have negative or complex entries, if any of the gates in the circuit do. For the case $\tilde A = U \mathrm{e}^{-1/T}$, this again suggests that the BQP-completeness of estimating entries of matrix powers $\tilde A^m$ is associated with whether $\tilde A$ has entries apart from non-negative reals.
Given this, considered as a special case of HHL which is motivated by the comparison to the problem of Janzing and Wocjan, I'd like to know: is HHL still BQP-complete if all of the entries of $A$ and $\lvert b \rangle$ are in $\\{0,1\\}$ ?
|
https://quantumcomputing.stackexchange.com/questions/13404/is-hhl-still-bqp-complete-when-the-matrix-entries-are-only-in-0-1
|
[
"complexity-theory",
"hhl-algorithm",
"bqp"
] | 14 | 2020-08-19T17:26:40 |
[
"(Having said that, seeing how having entries of {0,1} for $A$ is still not the same as having {0,1} entries for $A^{-1}$ or a matrix $\\tilde A$ whose powers you would like to learn about, I still think that having non-negative entries for $A$ itself is a bit of a red herring... once you take the inverse of $A$, negative entries can still arise, shedding no further light on the question quantum computational difficulty without destructive interference.)",
"I've made some changes. I think I understood your question better once I read it with a different emphasis, and I've tried to amplify that emphasis.",
"Thanks, could you edit the question to address your concerns? I’d like an answer to the question in the title...",
"I'd be willing to have a go at editing the question, if what you'd like is something specifically addressing the case where A and |𝑏⟩ have {0,1} entries, together with some remarks putting the question in context. As it stands, it still feels a bit as though you're asking one thing because you want to know the answer to something else.",
"So, you've added some commentary about the role of negative entries, but the main question (the title, the reasonable question towards the end) is still about {0,1} entries. Also: in your recent edit, it's not clear that the claim about $A = I - U\\exp(-1/T)$ is what you intend to claim (do you mean $A^{-1}$ by chance?), or that the statement that you might like to make is correct (what about the special case where $U$ is constructed only from classical reversible gates?).",
"You're asking two different questions. The question about whether HHL is BQP-complete, if all the entries of A and |𝑏⟩ are in {0,1}, is clear enough. But you're never going to construct A = I - U exp(-1/T) and still have coefficients in {0,1}, so it's not clear how that construction could play any role. So, are you asking about the role of the minus sign in the construction, or are you asking about constraining the values of A?"
] | 6 |
Technology
| 0 |
481
|
quantumcomputing
|
Can you programatically check whether a given set of gates is universal?
|
I am wondering if there is an automated way to determine whether a given set of quantum operations is universal.
More precisely, given a set of 1 and 2 qubit gates, can we write a program to determine whether this constitutes a universal gate set? If so, how might we do this?
**EDIT:** To clarify I'm interested in both approaches which allow exact replacements (as shown below) and approaches which allow approximating any unitary to some finite precision. Perhaps restricting the problem by not allowing arbitrary rotations in the input gateset could make the problem more tractable I'm not sure.
If I was given a set of quantum gates I would try to use the gates I'm given to implement a well known universal gateset.
Take this artificial example...
\begin{equation} S_0 = \\{\text{H}, \text{Rx}(\alpha), \text{CZ}\\} \end{equation}
I know I can write any single qubit operation with $\\{\text{H}, \text{Rx}(\alpha)\\}$ as I can reach any point on the Bloch sphere with 3 parameterised rotations in 2 directions (I can implement $\text{Rz}$ in terms of $\text{H}$ and $\text{Rx}$).
From here it's well known that an arbitrary single qubit rotation along with a $\text{CX}$ gate is sufficient for universality and I can realise a $\text{CX}$ using a $\text{CZ}$ with Hadamards on the target qubit. Therefore the set $S_0$ is a universal gate set.
When I try to think of a way to automate this process of using the provided gates to implement a well known universal gateset I'm not sure where to start. It certainly seems like a hard problem.
|
https://quantumcomputing.stackexchange.com/questions/32408/can-you-programatically-check-whether-a-given-set-of-gates-is-universal
|
[
"quantum-gate",
"universal-gates",
"transpile"
] | 9 | 2023-05-02T13:13:45 |
[
"I came across this paper, and I think this will be useful to you.",
"It might be an incomplete analogy but - we can't square the circle with a ruler and a compass; however, Archimedes taught us that we can get arbitrarily close, by inscribing and circumscribing polygons. With that in mind, can the ruler and compass alone get arbitrarily close to any well-defined point on the plane?",
"i.e. you could restrict to a finite set of parameterised gates rather than doing general single qubit rotations.",
"Interesting. I would have guessed that just verifying that a gateset can apporximate any n qubit unitary would be easier than exactly recreating any gate. Why might the approximate version using a finite set be harder to tackle?",
"@Callum That may be the harder case!",
"@DaftWullie . I suppose both cases are of interest to me. Is there a way to check if a gateset is approximately universal up to some $\\epsilon$?",
"Thanks @Mark S. indeed this other post is relevant. I think I’d need to read around a bit more to understand the discussion",
"Are you asking specifically about the case where you can exactly recreate any gate you want (e.g. the gate sets you've mentioned) or would finite gate sets achieving the target gate with arbitrary accuracy also fall within your interest?",
"See this question and answer -cstheory.stackexchange.com/questions/11298/…"
] | 9 |
Technology
| 0 |
482
|
quantumcomputing
|
Better "In-Place" Amplification of QMA
|
$\def\braket#1#2{\langle#1|#2\rangle}\def\bra#1{\langle#1|}\def\ket#1{|#1\rangle}$ In [MW05](https://arxiv.org/abs/cs/0506068) the authors demonstrate so-called "in-place" amplitude amplification for QMA, exhibiting a method for Arthur to amplify his success probability without requiring any increase in the size of Merlin's witness state. Call the original machine $M$ and the amplified machine $M'$.
Suppose that $x$ is the input, the original machine is $M(x,w)$ and the amplified machine is $M'(x,w)$. The approach of MW05 does not guarantee that a witness state that was in the accepting set for $M(x,\cdot)$ (i.e. that made $M$ accept input $x$ with probability exceeding, say, $\frac{2}{3}$) is still in the accepting set for $M'(x, \cdot)$ (i.e. those states that make $M'(x, \cdot)$ accept with amplified probability). I explain why I think that it's actually not possible to make their method do this below the line.
**Q: Is there a way to perform amplification of QMA machines without increasing the length of Merlin's witness and while also guaranteeing that all initially valid witnesses for a given input stay valid witnesses for this input?**
* * *
Without explaining too much context and using their notation, the issue that seems to arise is that MW05 first proves that their approach works for states that are eigenvectors of $Q$. This is good enough for completeness because if there's a state that accepts with probability $p \geq a$ then there's an eigenvector with success probability at least $p$. However, I don't think this can be used to show that any "good" witness also accepts w.h.p. after amplification.
In general a "good" witness $\ket{\psi}$. will be some linear combination of eigenvectors $\sum_j \alpha_j\ket{\psi_j}$, some of which are "good" and have acceptance probability $\geq a$ and others of which are "bad" and have acceptance probability $\leq b$. Let $S$ be the set of "good" witness eigenvectors. Then, once we amplify, our success probability is roughly (for $r$ large enough I guess)
$$\sum_{j \in S} |\alpha_j|^2(1-2^{-r}).$$
In general $\sum_{j \in S} |\alpha_j|^2$ isn't $1$ so we're in trouble. In the worst case of witness eigenvectors, we can even construct a "good" witness $\ket{\psi}$ that after $r$-rounds of amplification accepts with probability roughly $\frac{a-b}{1-b}(1-2^{-r}) \leq \frac{1}{2}$ for $(a,b) = (\frac{2}{3}, \frac{1}{3})$.
|
https://quantumcomputing.stackexchange.com/questions/8586/better-in-place-amplification-of-qma
|
[
"quantum-algorithms",
"complexity-theory",
"qma"
] | 8 | 2019-10-27T15:47:51 |
[] | 0 |
Technology
| 0 |
483
|
quantumcomputing
|
Qubit fidelity of DWAVE device
|
Since DWAVE quantum device is constructed using superconducting flux qubits, each qubit cannot be produced identically so that the fidelity of the qubit must be different. DWAVE only provides the information of their devices in terms of number of qubits, couplers, etc without any calibration data of each qubit on their [website](https://www.dwavesys.com/solutions-and-products/systems/).
I was wondering if we can find some information about the qubit fidelity of DWAVE machine. Since the number of qubits is quite huge, I assume it's time-consuming to calibrate the device and methods like randomized benchmarking are not applicable anymore. Is there any specific calibration method for that?
|
https://quantumcomputing.stackexchange.com/questions/23916/qubit-fidelity-of-dwave-device
|
[
"experimental-realization",
"fidelity",
"d-wave"
] | 8 | 2022-02-02T07:43:05 |
[] | 0 |
Technology
| 0 |
484
|
retrocomputing
|
How much did Atari pay for GEM?
|
Atari licensed Digital Research's GEM graphic user interface for the ST. As <https://www.filfre.net/2015/04/the-68000-wars-part-2-jack-is-back/> puts it:
> And of course in the wake of the Macintosh the ST simply had to ship with a mouse and an operating system to support it.
> It was this latter that presented by far the biggest problem. While the fairly conservative hardware of the ST could be put together relatively quickly, writing a modern, GUI-based operating system for the new computer represented a herculean task. Apple, for instance, had spent years on the Macintosh’s operating system, and when the Mac was released it was still riddled with bugs and frustrations. This time around Tramiel wouldn’t be able to just slap an archaic-but-paid-for old PET BASIC ROM into the thing, as he had in the case of the Commodore 64. He needed a real operating system. Quickly. Where to get it?
> He found his solution in a very surprising place: at Digital Research, whose CP/M was busily losing its last bits of business-computing market-share to Microsoft’s juggernaut MS-DOS. Digital had adopted an if-you-can’t-beat-em-join-em mentality in response. They were hard at work developing a complete Mac-like window manager that could run on top of MS-DOS or CP/M. It was called GEM, the “Graphical Environment Manager.” GEM was merely one of a whole range of similar shells that were appearing by 1985, struggling with varying degrees of failure to bring that Mac magic to the bland beige world of the IBM clones. Also among them was Microsoft’s original Windows 1.0 — another product that Tramiel briefly considered licensing for the ST. Digital got the nod because they were willing to license both GEM and a CP/M layer to run underneath it fairly cheap, always music to Jack Tramiel’s ears.
Just how cheap was it? How much did Atari pay DR? And what sort of terms were involved?
|
https://retrocomputing.stackexchange.com/questions/15377/how-much-did-atari-pay-for-gem
|
[
"history",
"atari",
"atari-st"
] | 10 | 2020-06-28T21:34:26 |
[
"@tofro - details of other similar deals (eg Microsoft's licensing of SCP's 86-DOS) are known. It's plausible that details of this deal have come to light via a similar route.",
"Sadly, I suspect that the intersection of “people who would have even known at the time” (C-suite, accountant) and “people who care enough about old technology enough to visit Retro.SO” is very, very small. Of the intersection, the chances that they will remember what the negotiated price was is probably zero. Engineers would have been told “we licensed GEM, take care of the integration” but they would not have been told the licensing cost because it wasn’t relevant, NDA would likely impose need-to-know basis, and it was none of the engineer’s business to know.",
"@tofro I would normally expect NDA's to have expired after three and a half decades with the companies no longer in business. If they are really for life in this case, that in itself would be an interesting historical fact.",
"@user there were several companies selling their home/soho machines with GEM. Think Philips Yes and alike.",
"Who do you think could answer this? Everyone who really could know is either dead or very probably still under a lifetime NDA...",
"Would be interesting to know what Amstrad paid for it too. It was included with the PC1512."
] | 6 |
Technology
| 0 |
485
|
retrocomputing
|
What was IBM's internal Specification Language of the 1980s?
|
Within IBM's internal Development community, there was a move in the 1980s to bring our skills up to date. As part of this, we were introduced to a specification language, independent of the programming languages of the time (PL/S and Basic Assembler for example), in which a specification would be implemented. This specification language, as I recall, embodied set theory and logic in a type-safe context.
In fact, in the IBM Hursley Lab we eventually chose to use the Z notation from the Programming Research Group at Oxford University. This was perhaps more strictly mathematical than the IBM language - part of a Formal Methods approach.
However, I spent quite a bit of time with the IBM specification language and I would very much like to know if anyone recalls what it was called and what happened to it.
It had a “specification checker” for type consistency etc and I remember it very fondly, before getting immersed in the Z notation.
|
https://retrocomputing.stackexchange.com/questions/25868/what-was-ibms-internal-specification-language-of-the-1980s
|
[
"history"
] | 10 | 2022-12-14T00:21:28 |
[
"Thanks @davidbak I’m not thinking of VDM which, like Z, is more mathematically formal than the IBM language I am searching for.",
"See if this article rings a bell - dl.acm.org/doi/abs/10.1145/356596.356598 (PDF is freely available here)",
"I'm thinking it was the \"Vienna Definition Language\"? foldoc.org/Vienna+Definition+Language - see also en.wikipedia.org/wiki/Vienna_Development_Method#History"
] | 3 |
Technology
| 0 |
486
|
stackoverflow
|
Ограничения на поиск пользователей через users.search api vk
|
У api вконтакте есть ограничение - 3 запроса в секунду. Однако у `users.search` есть какое-то своё ограничение на количество вызовов.
> Помимо ограничений на частоту обращений, существуют и количественные ограничения на вызов однотипных методов. По понятным причинам, мы не предоставляем информацию о точных лимитах.
Нужно найти 1000 человек в соцсети (клиенты компании). Если api бы работало хорошо, это было бы 300 секунд. А что делать с тем, что на N-м запросе api выдаёт 0 найденных? Похоже, что N-порядка десятков.
Другие методы работают, а этот выдаёт 0. Причём даже если попытаться поискать людей просто в браузере - тоже 0 найденных.
Кто сталкивался, поясните, надолго ли происходит такое отключение поиска. И может есть какое-то время паузы, выше которого поиск всегда работает и возвращает результаты?
[Проверка через execute тут](https://vk.com/dev/execute "Проверка через execute тут")
var found = API.users.search({"q":"Иванов Иван"});
return found;
Запуск этого кода даёт `response: { count: 0, items: [] }`, когда `users.search` вдруг перестаёт работать.
|
https://ru.stackoverflow.com/questions/451645/%d0%9e%d0%b3%d1%80%d0%b0%d0%bd%d0%b8%d1%87%d0%b5%d0%bd%d0%b8%d1%8f-%d0%bd%d0%b0-%d0%bf%d0%be%d0%b8%d1%81%d0%ba-%d0%bf%d0%be%d0%bb%d1%8c%d0%b7%d0%be%d0%b2%d0%b0%d1%82%d0%b5%d0%bb%d0%b5%d0%b9-%d1%87%d0%b5%d1%80%d0%b5%d0%b7-users-search-api-vk
|
[
"javascript",
"vkontakte-api"
] | 8 | 2015-09-17T05:51:12 |
[
"Возможный дубликат вопроса: Ограничения VK-APi",
"Но нельзя не согласиться с тем, что эта мера с неизвестным лимитом сильно портит жизнь и тем, кто готов играть по правилам. Видимо, выбирая защиту от злоупотреблений, недовольством соблюдающих правила пользователей решили пренебречь.",
"Если допустимое кол-во запросов будет известно заранее, то ботописатели обойдут ограничение, путём использования в парсере неограниченного количества учётных записей, коих в сети можно покупать, хоть пачками. А тут получается, что возврат нулевого значения не гарантирует в любой момент времени, что поиск не обнаружил данные по запрашиваемой строке. Может они есть, а может аккаунт уже забанен. Это ведёт к тому, что нужно выполнять отдельный запрос с заранее проверенным на корректность результатом на каждый нулевой ответ. Это конечно позволит проверить достоверность ответа, но сильно снизит КПД.",
"@alexis031182 честно говоря, из-за этой неоднозначности не очень хочется с ними работать, не беру работу по их апи больше. Программирование и нечёткие правила несовместимы.",
"Похоже, что не только users.search подвержен ограничению, но и wall.search. Проверено, \"банят\" довольно быстро с теми же симптомами, что и в вопросе. К сожалению, не удалось вычислить момент, с какого по счёту запроса это началось. Вполне вероятно, что audio.search, а также video.search тоже весьма ограничены."
] | 5 |
Technology
| 0 |
487
|
stackoverflow
|
Максимально возможное заполнение в клеточном автомате "Life"
|
Меня интересует алгоритм вычисления максимально возможного количества "живых" клеток на поле размером 100х100. Предполагается, что это поле - развернутый тор. Стартовое и конечное положения меня не интересуют. Но это должно быть возможное игровое состояние - т.е. состояние, соответствующее правилам (а не, например, просто заполненный квадрат 100x100). Интересует именно максимум. Возможно, кто-то логически объяснит, что может быть именно такое-то число и не больше ни меньше.
Возможно, многие знают правила игры. Но я их повторю:
> 1) в пустой (мёртвой) клетке, рядом с которой ровно три живые клетки, зарождается жизнь;
>
> 2) если у живой клетки есть две или три живые соседки, то эта клетка продолжает жить;
>
> 3) в противном случае (если соседей меньше двух или больше трёх) клетка умирает («от одиночества» или «от перенаселённости»)
**Уточнение:** Дабы не было никому обидно (и были понятны комменты), правку вношу в виде уточнения, а не меняя непосредственно сам вопрос.
Мне необходимо реальное промежуточное состояние. То, которое может быть достигнуто в принципе. При этом, хотелось бы знать максимально возможное количество живых особей в популяции. Да, действительно, это состояние может быть конечными или цикличным. Но меня не интересует стартовое состояние, когда оно соответствует правилам старта, но, на самом деле, оно не может быть получено иным путем.
Даже скажу больше... возможно, это состояние (состояние максимума популяции для квадрата 100x100) может быть достигнуто из расчета, что первоначальный квадрат был больше. Хотя желательно, чтобы он был ограничен в размерах и был тором.
Отвечая на вопрос, что значит _"возможное игровое состояние"_ отмечу, что в моем понимании, стартовое состояние является как бы предигровым состоянием или стартовым состоянием, но не состоянием, полученным в процессе игры. _"Возможное игровое состояние"_ в данном случае мной понимается как состояние, полученное в процессе игры.
Возможно, кто-то и не согласен с моим пониманием игрового состояния, но такое оно и есть. Представьте, что гости собираются и рассаживаются за стол (даже уже сели). Но это не застолье. Вот как-то так.
Если предлагаемая популяция циклична, то, может быть, имеет смысл сократить размер поля до 10x10?
|
https://ru.stackoverflow.com/questions/502844/%d0%9c%d0%b0%d0%ba%d1%81%d0%b8%d0%bc%d0%b0%d0%bb%d1%8c%d0%bd%d0%be-%d0%b2%d0%be%d0%b7%d0%bc%d0%be%d0%b6%d0%bd%d0%be%d0%b5-%d0%b7%d0%b0%d0%bf%d0%be%d0%bb%d0%bd%d0%b5%d0%bd%d0%b8%d0%b5-%d0%b2-%d0%ba%d0%bb%d0%b5%d1%82%d0%be%d1%87%d0%bd%d0%be%d0%bc-%d0%b0%d0%b2%d1%82%d0%be%d0%bc%d0%b0%d1%82%d0%b5-life
|
[
"алгоритм"
] | 8 | 2016-03-14T07:25:23 |
[
"Комментарии не предназначены для расширенной дискуссии; разговор перемещен в чат."
] | 1 |
Technology
| 0 |
488
|
chemistry
|
Dry water using graphite
|
[Dry water](https://en.wikipedia.org/wiki/Dry_water) or "powdered water" is essentially a bunch of extremely small water droplets surrounded by $\ce{SiO2}$.
Some time ago, I was messing around and mixed some powdered graphite with water. (The graphite was obtained from a pencil, so it was not pure. Also I mixed the two substances with a stick, not with a high-speed blender.) When a droplet of this was splashed onto the table, it could be blown around with air and even held on the hand without breaking, until it was squished.
The important part of this is, that that droplet could be placed back into the original mixture of water and graphite powder, and it would roll around on the surface.
So does anyone know if it's possible to use powdered graphite rather than silica particles to make dry water? If is is, what properties are different from the ordinary powdered water?
|
https://chemistry.stackexchange.com/questions/61838/dry-water-using-graphite
|
[
"water",
"mixtures"
] | 7 | 2016-10-30T06:48:15 |
[
"Graphite for pencils is mixed with clay, which is largely composed of silicates. I don't know whether pure graphite powder would display the same behavior you describe.",
"I may end up doing something similar to this for a school project. If I decide to mix the graphite with water instead of ink, I will measure its conductance. I could post my results here, maybe.",
"@Ivan But the 'dry water' uses hydrophobic silica particles (surface modified). I think that nanographite would be a suitable substitute.",
"Silica is highly hydrophilic, graphite is not quite like that."
] | 4 |
Science
| 0 |
489
|
chemistry
|
Mathematical models of oscillatory chemical reactions
|
I am a mathematician working on real-life models in ordinary differential equations. I want to know if there are any models of oscillatory chemical reactions that consist of three ordinary differential equations where one variable is much slower than the other two. In particular I am interested in bursting behavior, which consists of alternating trains of fast oscillations with periods of rest.
I have been searching and I couldn't find what I am looking for. I found about the Belousov-Zhabotinsky reaction, but in this case we have one fast variable and two slow variables, while I'm looking for two fast variables and one slow variable.
|
https://chemistry.stackexchange.com/questions/166898/mathematical-models-of-oscillatory-chemical-reactions
|
[
"physical-chemistry",
"kinetics",
"theoretical-chemistry"
] | 7 | 2022-08-05T08:27:40 |
[
"related? wrap.warwick.ac.uk/60495/1/WRAP_computation-02-00047.pdf",
"Related: mattermodeling.stackexchange.com/q/8812/5",
"Somewhat related"
] | 3 |
Science
| 0 |
490
|
chemistry
|
Interaction of trifluoroacetates with acetylcholinesterase
|
There exists a substance called TMTFA, or 3-(_N,N,N_ -Trimethylammonio)-2,2,2-trifluoroacetophenone. It is known for being able to inhibit acetylcholinesterase at femtomolar concentrations. The TMTFA-AChE adduct resembles the tetrahedral transition state through which the hydrolysis of acetylcholine by the enzyme normally proceeds, and this adduct is stabilized by the electron-withdrawing trifluoromethyl group present in the TMTFA molecule. This inhibition is reversible.
While there have been studies regarding trifluoroacetophenones and their interactions with AChE, I haven't been able to find studies exploring the interactions between AChE and trifluoroacetates, such as 3-(_N,N,N_ -trimethylammonio)phenyl trifluoroacetate or 2,2,2-trifluoroacetylcholine. Would these, and other, esters of trifluoroacetic acid inhibit AChE or be hydrolyzed normally? If it's the former, then what are the typical inhibitory concentrations of such esters? What is the shape of the adduct of the ester with AChE? How long would they remain bound to the enzyme? Have any studies been done regarding the bioactivity of such esters?
### References
1. Nair, H. K.; Seravalli, J.; Arbuckle, T.; Quinn, D. M. Molecular Recognition in Acetylcholinesterase Catalysis: Free-Energy Correlations for Substrate Turnover and Inhibition by Trifluoro Ketone Transition-State Analogs. _Biochemistry_ **1994** , _33(28)_ , 8566–8576. DOI: [10.1021/bi00194a023](https://doi.org/10.1021/bi00194a023).
2. Harel, M.; Quinn, D. M.; Nair, H. K.; Silman, I.; Sussman, J. L. The X-Ray Structure of a Transition State Analog Complex Reveals the Molecular Origins of the Catalytic Power and Substrate Specificity of Acetylcholinesterase. _J. Am. Chem. Soc._ **1996** , _118(10)_ , 2340–2346. DOI: [10.1021/ja952232h](https://doi.org/10.1021/ja952232h).
|
https://chemistry.stackexchange.com/questions/135747/interaction-of-trifluoroacetates-with-acetylcholinesterase
|
[
"organic-chemistry",
"biochemistry",
"proteins",
"esters",
"enzymes"
] | 5 | 2020-06-24T21:41:08 |
[
"According to Ref.2, TMTFA binds titly to AcE from a Pacific electric ray, Torpedo californica. It might not do the same to Human AcE. I believe your intention is for inhibitors of Human AcE."
] | 1 |
Science
| 0 |
491
|
chemistry
|
Reaction of Rubidium with vacuum system viewport
|
I have a vacuum system ($<1\times10^{-7}$ mbar) filled with Rubidium ($^{87}$Rb) vapour, at room temperature.
We also have a viewport near the Rubidium source, made of a stainless steel flange and a glass substrate, connected with a [Kovar](https://en.wikipedia.org/wiki/Kovar) alloy.
We are seeing potential degradation of the seal, which we do not see on other parts of the system. The only difference is the Nickel and Cobalt based Kovar alloy, not present anywhere else.
What are the reaction rates of Nickel and/or Cobalt with Rubidium?
|
https://chemistry.stackexchange.com/questions/81551/reaction-of-rubidium-with-vacuum-system-viewport
|
[
"everyday-chemistry",
"home-experiment"
] | 5 | 2017-08-21T04:23:40 |
[
"btw, thanks to ability of rubidium to form suboxides even tiniest amount of oxygen may bind a lot of rubidium.",
"Please, check the mark of the glass and if it is suited for work with rubidium in this particular settings. In general, glasses are oxides that can potentially react with alkali metals in right circumstances. I see no reason for them to react with nickel/cobalt alloy. However, rubidium might react with oxide layer on the surfaces of this alloy and/or any dirt left on the seal (and glass, and any dirt left on the glass) and any passing air if the seal is... not good enough."
] | 2 |
Science
| 0 |
492
|
hsm
|
Whence “homomorphism”, “homomorphic”?
|
The [kernel](https://hsm.stackexchange.com/questions/2149/what-came-first-the-kernel-from-vector-spaces-or-from-group-theory) question leads to another : Today, **_homomorphism_** (resp. _isomorphism_) means what Jordan ([1870](https://archive.org/stream/traitdessubsti00jorduoft#page/56)) had called _isomorphism_ (resp. _[holoedric](https://hsm.stackexchange.com/questions/3108/jordan-called-isomorphisms-iso-and-homomorphisms-iso-holoedriques-and-iso) isomorphism_). How did the switch happen?
* “Homomorphic” appears e.g. in de Séguier ([1904](https://www.emis.de/cgi-bin/JFM-item?36.0187.02), [pp. 65–66](https://archive.org/stream/thoriedesgroup00sguoft#page/65)):
> (...) supposons entre les groupes $\mathrm A$ et $\mathrm B$ une correspondance telle qu’à chaque élément de $\mathrm A$ réponde un élément au moins de $\mathrm B$ et à chaque élément de $\mathrm B$ un élément au moins de $\mathrm A$ et que si $a_i$ de $\mathrm A$ et $b_i$ de $\mathrm B$ se correspondent, $a_ia_k$ et $b_ib_k$ se correspondent aussi. On dit que $\mathrm A$ et $\mathrm B$ sont _homomorphes_.
* “Homomorphism” (as _property_ of being homomorphic) appears e.g. in Loewy ([1912](https://www.emis.de/cgi-bin/JFM-item?43.0199.02), [p. 198](https://archive.org/stream/festschriftheinr06webeuoft#page/198)):
> §1 (...) untersucht den Homomorphismus zweier abstrakter Gruppen (...).
* “Homomorphism” (as _map_ between groups) appears e.g. in Hopf ([1928](https://www.emis.de/cgi-bin/JFM-item?54.0610.02), [p. 128](http://www.digizeitschriften.de/dms/img/?PID=GDZPPN002507641&physid=phys139)):
> 4) Unter einem Homomorphismus der Gruppe $\mathfrak G$ in die Gruppe $\mathfrak H$ verstehen wir eine eindeutige Abbildung $f$ von $\mathfrak G$ auf einen echten oder unechten Teil von $\mathfrak H$, bei der stets $f(x+y)=f(x)+f(y)$ ist.
Are these the earliest occurrences?
|
https://hsm.stackexchange.com/questions/6460/whence-homomorphism-homomorphic
|
[
"terminology",
"abstract-algebra",
"group-theory"
] | 9 | 2017-08-26T17:04:12 |
[
"Now cross-posted: mathoverflow.",
"Homomorphism is etymologically correct in the sense that the structures of two groups exhibit a degree of similarity when one can map into the other (trivial cases apart). Isomorphism is then more accurately used to mean \"congruent\" structure. (\"Isos\" is more commonly used to mean equal, but Euclid also uses it for congruent.)",
"The following text notes the use of homomorphism by de Séguier in 1904, and then states that the term was introduced by Klein without giving a reference. books.google.ca/…"
] | 3 |
Science
| 0 |
493
|
hsm
|
Who was the first to use the "does not exist" sign ∄?
|
Who was the first to use the "does not exist" sign ∄? I'm aware that Giuseppe Peano originated serifed ∃ and, moreover that Whitehead and Russell repurposed Peano's serifed ∃; I'm also aware that Gerhard Gentzen introduced the ∃ sans serif (and used it like Russell and Whitehead rather than like Peano). Yet, I cannot find who was the first to use ∄ as ~∃ to mean "there does not exist". Any idea? Thank you.
|
https://hsm.stackexchange.com/questions/7181/who-was-the-first-to-use-the-does-not-exist-sign-%e2%88%84
|
[
"terminology",
"notation",
"mathematical-logic"
] | 9 | 2018-03-26T14:01:36 |
[] | 0 |
Science
| 0 |
494
|
hsm
|
Who first defined polynomials as sequences?
|
> **Question 1.** When did the modern definition of a **polynomial** (as a sequence of coefficients, with multiplication defined by $\left(ab\right)_n = \sum\limits_{k=0}^n a_k b_{n-k}$) emerge?
Let me clarify: People have been working with some notion of polynomials for centuries, but mostly without a rigorous concept of what a polynomial is. From what I understand, "equations" rather than polynomials were the focus, and demarcating the precise extent of what an "equation" is was secondary to actually solving equations of given, fairly specific types. When the need for a rigorous definition became clear, it seems that the go-to solution was to define a polynomial as a polynomial **function** (e.g., §1 of [Roland Weitzenböck, _Invariantentheorie_ , 1923](https://quod.lib.umich.edu/cgi/t/text/text-idx?c=umhistmath;idno=ABV0733)). This worked well for polynomials over $\mathbb R$ or $\mathbb C$, but not so much for polynomials over finite fields (which may be why E. H. Moore had to define $\mathbb{F}_{p^n}$ as a quotient ring of a polynomial ring over $\mathbb Z$ rather than of a polynomial ring over $\mathbb{F}_p$ [in his 1893 talk](https://projecteuclid.org/download/pdf_1/euclid.bams/1183407788)).
What I call the "modern definition" of a polynomial is one of the following two definitions:
* either as an infinite sequence $\left(a_0, a_1, a_2, \ldots\right)$ of coefficients (with all but finitely many $n$ satisfying $a_n = 0$), with addition defined entrywise and multiplication defined by the $\left(ab\right)_n = \sum\limits_{k=0}^n a_k b_{n-k}$ formula (and the indeterminate defined as the sequence $\left(0,1,0,0,0,\ldots\right)$ rather than being some mythic "symbol" or "indeterminate value" or "variable"),
* or as the monoid ring of the additive monoid $\left\\{0,1,2,\ldots\right\\}$.
The second of these two definitions appears in §15 of B. L. van der Waerden, _Moderne Algebra I_ , 2te Auflage 1937. (I can't check the 1st edition, as I don't have it.) This gives a lower bound on the age of the modern definition. As for an upper bound, I am perplexed. Nicolas Bourbaki's _Elements of the History of Mathematics_ grazes the question on its page 82:
> In all this research, the fields that arise consist of "concrete" elements in the sense of classical mathematics - (complex) numbers or functions of complex variables. 32 But already Kronecker, in 1882, takes full account of the fact (obscurely sensed by GaUBB and Galois) that "indeterminates" only play the role in his theory of the basis elements of an algebra, and not that of variables in the sense of Analysis ([186 a], v. II, pp. 339-340); and, in 1887, he develops this idea, linked to a vast programme that aims at nothing less than recasting all mathematics by rejecting all that cannot be reduced to algebraic operations on the integers. It is on this occasion that, taking up an idea of Cauchy ([56 a], (1), v. X, pp. 312 and 351) who had defined the field $\mathbb C$ of complex numbers as the field of remainders $\mathbb R\left[X\right]/\left(X^2+1\right)$, Kronecker shows how the theory of algebraic numbers is completely independent of the "fundamental theorem of algebra" and even of the theory of real numbers, all fields of algebraic numbers (of finite degree) being isomorphic to a field of remainders $\mathbb Q\left(X\right)/\left(f\right)$ ($f$ an irreducible polynomial over $\mathbb Q$)([186 a], v. 1111, pp. 211-240).
Following the references here, I see some signs of the modern definition slowly dawning in the 19th Century: [Note: "Polynomials" are often called "forms" before ca. the 1930s, particularly when they are homogeneous.]
* I don't know what exactly Cauchy had done; the [56 a] reference goes to his Oeuvres, which I don't have.
* The first Kronecker reference goes to [his _Grundzüge einer arithmetischen theorie der algebraischen Grössen_ (1882)](https://archive.org/details/grundzgeeinerar01krongoog/page/n129), where he talks of "veränderliche oder unbestimmte Grössen" but never constructs any.
* [J. Molk, _Sur une notion qui comprend celle de la divisibilité et sur la théorie générale de l'élimination_ , Acta Math. **6** (1885), pp. 1--165](https://projecteuclid.org/euclid.acta/1485888021), spends its section 2 (and maybe the whole Chapitre I?) arguing about the difference between variables and indeterminates. Alas, the argument appears to veer into philosophical terrain rather quickly, which puts it beyond my French comprehension skills; thus I have no idea what conclusion he actually comes to.
* [H. Weber, _Die allgemeinen Grundlagen der Galois'schen Gleichungstheorie_ , Mathematische Annalen **43** (1893), pp. 521--549](https://eudml.org/doc/157689) tries to define polynomials in its §3 (after defining the notions of groups and fields in ways that are equivalent to their modern definitions). The definition pays obvious tribute to the idea that polynomials should not be functions; in particular it explicitly says that two polynomials are understood to be equal if and only if their respective coefficients are equal (rather than their values being equal). However, a vague notion of "expressions of the form $\Phi\left(x,y,z,\ldots\right) = \sum a x^r y^s z^t \cdots$" underlies this definition, and (e.g.) the multiplication is never explicitly defined (nor its associativity proven). (To this day, some algebra textbooks geared towards non-math majors work on this level.)
So my question is: Who completed this definition? Weber (later)? Kronecker? Dedekind? Noether? van der Waerden? And while at that:
> **Question 2.** Who defined formal power series?
>
> **Question 3.** Who defined polynomials in noncommutative indeterminates?
These are litmus tests for Question 1; a rigorous definition of polynomials needs only a few trivial modifications to define formal power series, and a definition of noncommutative polynomials is not far away either.
The concept of a polynomial is, in a way, similar to the number $0$: It's an idea that, on its own, appears pedantic and meatless. But once it is established, it becomes a building block of a whole discipline that no one would want to be missing. (19th Century algebraists like Sylvester tend to use the unique factorization property of a polynomial ring without ever explaining what it is that they are factoring; from a modern perspective, this is a gaping hole in their proofs.) My hope is that, as this specific matter is much younger than the number $0$, we may have better clues to its authors.
|
https://hsm.stackexchange.com/questions/9710/who-first-defined-polynomials-as-sequences
|
[
"mathematics",
"abstract-algebra"
] | 8 | 2019-06-07T14:43:53 |
[
"Not in the modern sense, but that can be said about most of algebra until the late 18th century. Hudde further treated polynomials purely algebraically in the 17th. Dieudonne, before reinterpreting Euler's manipulations in terms of formal power series, states the following:\"These series appear in print in Hilbert's Grundlagen der Geometrie, apparently for the first time\".",
"Interesting! This is pretty much the modern definition. I take it he didn't prove anything, though? (The question is nontrivial, because he had something very much resembling induction in his work, so it's not like the toolkit was entirely missing.)",
"What you call the \"modern definition\" was the original one given by al-Karaji and al-Samawal back in the 12th century. The latter wrote powers and the corresponding coefficients as columns of a table, and gave a multiplication rule equivalent to the convolution formula (al-Karaji's descriptions were verbal and more obscure). He even allowed negative powers (hence Laurent polynomials), and gave an algorithm for the \"synthetic division\". See e.g. Katz, History of mathematics, 9.3.3"
] | 3 |
Science
| 0 |
495
|
proofassistants
|
Unintentionally proven false theorem with type-in-type outside logic and foundations?
|
We are all familiar with Russell's paradox, and [it is known](https://proofassistants.stackexchange.com/a/1220) that Per Martin-Löf proved that type-in-type is normalizing and consistent (which is false), by accidentally using an assumption in his meta-theory that is essentially type-in-type. But all these arise in the areas of logic and foundations. Has anyone proven some statement Q by accidentally using some type-in-type assumption, without being aware that such an assumption is unsound, and such that Q can be shown to be surely false (say in a typical predicative type theory)?
The linked example would be considered to be under foundations. Here is another example that is not quite under logic or foundations but anyone who proves it will certainly be immediately aware that the type-in-type assumption is unsound: Let W be the type of all rooted (downward-directed) trees with no infinite (downward) path. Let T be a rooted tree whose root has exactly the members of W as children. Now T is in W...
So is there any example where the person who proved the result was still unaware (at least for a reasonable period of time) that the type-in-type assumption was unsound?
|
https://proofassistants.stackexchange.com/questions/1238/unintentionally-proven-false-theorem-with-type-in-type-outside-logic-and-foundat
|
[
"foundations",
"history",
"predicativity",
"universe",
"consistency"
] | 13 | 2022-04-04T07:40:29 |
[
"And negation is not even needed, nor is any notion at all about 'categories'. To see why, if type∈type, then let S be the 'type' of all types x such that ∀t∈{ 0 : x∈x } ( ⊥ ), and it is trivial to obtain ⊥ by constructive proof: Given any t∈{ 0 : S∈S }, we have S∈S and so ∀t∈{ 0 : S∈S } ( ⊥ ), hence ⊥. Therefore S∈S, and so ⊥. By the way, if we require a type's defining predicate to quantify over only predicative types, then we can have type∈type in a predicative system!",
"@AndrejBauer: Yes, but that has nothing to do with category theory; it is just plain foundational concerns, because it just comes down to saying that sets are closed under function types but classes are not (if you only have two levels). In turn, this is ultimately like Frege's Axiom V; because it is just another result of 'wishful thinking' that certain concepts have reifications. If people want to reason about any 'large' things without giving solid justification why those things can even be reified in the first place, then it's just like asking for Russel's paradox all over again.",
"Still running on vague memories, I think one of the pertinent observations was that “$f : A \\to B$ is epi” in a large category involves universal quantification over a class. Speaking type-theoretically, the type of epis in a category $C$ living in a universe $U$ might live outside $U$. So for instance, if we take the subcategory of epis in $C$, we've bumped up the universes. But ultimately, we'd have to find the specific objections to see in what way they're problematic.",
"@AndrejBauer: I vaguely recall reading some examples of that sort, yes, but to me those are due to wishful thinking way beyond higher-order arithmetic. Ultimately, what is the difference between those mistakes and Frege's Axiom V? The point is that a lot of these explorations were based on dubious axioms that arose out of logic and foundations, and were not things that mathematicians genuinely believed to be true in a platonic sense.",
"I vaguely remember Benabou, or perhaps Dobus, telling some cautionary tales about faulty reasoning in category theory, where mistakes can be made easily enough if one does not pay attention to class-set distinction. But I don't know the reference.",
"@AndrejBauer: Let me put it another way; if an example was actually utilized to obtain a theorem in the language of higher-order arithmetic that is believed to be incorrect, then I would agree that that obtained theorem is an actual example of the type I am looking for. If not, then I'm unlikely to buy that it is outside of logic and foundations.",
"Mike's example looks like it's \"just\" about type theory, but it actually has a much wider applicability.",
"I don't count Mike's example by the way, as it is literally about type theories, which is squarely in logic and foundations. After all, I did link to that thread in my question!",
"@AndrejBauer: It need not be in type theory. Naive set theory also has a type-in-type assumption, even if it is not called \"type\". I'm not intending to restrict answers to only type theories of a particular narrow tradition.",
"@MevenLennon-Bertrand: But did that result in any false theorem that was believed to be a good theorem?",
"Or in the glory era of early Unimath, when they decided to use type-in-type to avoid issues with universes? Which looks like the time to which Mike Shulman's example belongs.",
"Just about anyone who learns type theory nowadays knows about type-in-type. So if there is an example of what you're asking for, it would have to have taken place in the narrow period between Martin-Löf's type theory with type-in-type, and the realization that it's inconsistent.",
"Yes, that's the one I was thinking of!",
"@AndrejBauer is this the one: proofassistants.stackexchange.com/questions/1219/… ? I don't know if this fits the question, though: I would say it is outside of logic and foundation, but Mike Shulman says he does not know whether it holds or not, so it probably cannot \"be shown to be surely false\" with our current knowledge…",
"I seem to remember some discussion about accidental universe inconsistencies that were masked at first. Maybe Mike Shulman communicated them, I'll try to remember."
] | 15 |
Science
| 0 |
496
|
proofassistants
|
Rules for mutual inductive/coinductive types
|
Some proof assistants, like Agda and maybe Coq, allow families of mutually defined types, or nested definitions of types, in which some are inductive and others are coinductive. I have no idea what the type-theoretic introduction/elimination rules should be for such a family, and as shown in [this question](https://proofassistants.stackexchange.com/q/961/98) their behavior can be kind of unexpected. The implementation, I guess, allows general "matches" and "comatches", with a separate "termination/productivity checker"; but this is not a semantic explanation suitable for, say, finding category-theoretic models.
Has anyone written down an inference-rule presentation of a type theory including mutual or nested inductive/coinductive definitions?
|
https://proofassistants.stackexchange.com/questions/980/rules-for-mutual-inductive-coinductive-types
|
[
"type-theory",
"coinductive-type",
"inductive-type"
] | 12 | 2022-03-06T12:57:18 |
[
"I'm aware of Hening Basold's thesis. And Danielsson and Altenkirch's Mixing Induction and Coinduction has a long list of related work, some of which may have rules (e.g. the work on sized types).",
"I mean the 'partiality monad', which you can model as a HIT/QIT via the free ω-complete partial order on a type. As a mixed definition you try to define the same thing similarly to the coinductive definition of the extended natural numbers. Conceivably it might be better behaved than quotienting a coinductive type after the fact (which I think requires countable choice to be a monad).",
"What is \"$\\omega$-completion\"?",
"I might add that even if there's a more rigorous presentation of what Agda/Coq does, it'd probably also be nice to have something better. A while back it was observed that trying to define ω-completion as a mixed higher-inductive/coinductive definition gets you something contractible. But now I wonder if it's just because you can't write down the right thing in Agda (i.e. you really want uses of the higher constructor to be well-founded, but they aren't in Agda)."
] | 4 |
Science
| 0 |
497
|
biology
|
What's the difference between proliferation and diffusion when talking about changes in tumor density?
|
Cell proliferation and cell diffusion seem to be important quantities to estimate when trying to understand or measure tumor growth, but I don't really understand a) the difference between them or b) their relationship to tumor growth.
Cell proliferation refers to cellular subdivision. This doesn't necessarily mean tumor growth because something can subdivide but still have the same net mass, right?
Cell diffusion on the other hand, refers to changes in cell density. Supposing cell proliferation is constant and we have positive diffusion, that would mean that cells are 'spreading out' (ie the mass is less dense but bigger). Is this correct? Would positive diffusion be equivalent to tumor growth?
This question came up when reading [this paper](https://www.ncbi.nlm.nih.gov/pubmed/27164582). It talks about estimating diffusion and proliferation parameters in order to solve the reaction-diffusion equation which is, in turn, used to model tumor growth.
|
https://biology.stackexchange.com/questions/57119/whats-the-difference-between-proliferation-and-diffusion-when-talking-about-cha
|
[
"cell-biology",
"growth",
"differentiation",
"cancer"
] | 5 | 2017-03-08T10:29:49 |
[
"A tumor by definition is an abnormal proliferation of cells but I don't think diffusion has anything to do with cells actually diffusing. Rather, the carrying capacity of a tumor depends on such parameters as nutrients or oxygen, which must diffuse further inwards until they cannot reach cells. Hence, the core of large solid tumors tends to be necrotic. It's also my understanding that there is a natural pressure that forces older cells inwards to the core of the tumor, as the outside layers continue to divide and grow outwards, increasing the diameter of the tumor.",
"I would also like to see a reference to these terms if you have one."
] | 2 |
Science
| 0 |
498
|
stackoverflow
|
ある一定のダウンタイムがある並列システムを、特定の確率以上で常に必要並列数を上回らせるために必要な並列数は?
|
例えば web サービスは一般的にロードバランサーと並列数`N`で表されるワーカープロセスによって構築される場合が多いです。
今、あるワーカーが故障した時、そのワーカーが復帰するために必要な時間を`t`とします。ワーカーは、単位時間あたり`λ`の確率で故障し、その故障確率はそれまでの稼動時間に依らない、とします。
今、このサービスが問題なく稼動してワークロードをさばくためには、最低`m`個のワーカーがダウンしていない状態で稼動している必要があるとします。
このとき、確率論的に、ある一定の期間 `T` が与えられたとき、その期間の間のすべてのタイミングにおいて、上記の `m` 個のワーカーが稼動している確率 `p` が定義できると思い、これはこれまで出てきた `N`, `m`, `t`, `λ`, `T` についての関数になっていると思うのですが、その算出方法が分からずにいます。
# 質問
上記のような、ある並列システムが最低`m`の並列度を指定期間において達成している確率を求めたいのでが、これはどのようにすると求められますか?
これが分かることで、逆に算出された確率を信頼度とすることで、求められる信頼度に対して必要な `N` を求めたいと思い、質問しています。
|
https://ja.stackoverflow.com/questions/85441/%e3%81%82%e3%82%8b%e4%b8%80%e5%ae%9a%e3%81%ae%e3%83%80%e3%82%a6%e3%83%b3%e3%82%bf%e3%82%a4%e3%83%a0%e3%81%8c%e3%81%82%e3%82%8b%e4%b8%a6%e5%88%97%e3%82%b7%e3%82%b9%e3%83%86%e3%83%a0%e3%82%92-%e7%89%b9%e5%ae%9a%e3%81%ae%e7%a2%ba%e7%8e%87%e4%bb%a5%e4%b8%8a%e3%81%a7%e5%b8%b8%e3%81%ab%e5%bf%85%e8%a6%81%e4%b8%a6%e5%88%97%e6%95%b0%e3%82%92%e4%b8%8a%e5%9b%9e%e3%82%89%e3%81%9b%e3%82%8b%e3%81%9f%e3%82%81%e3%81%ab%e5%bf%85%e8%a6%81%e3%81%aa%e4%b8%a6%e5%88%97%e6%95%b0%e3%81%af
|
[
"数学"
] | 5 | 2022-01-01T23:26:31 |
[
"> \"N, m, t, λ, T についての関数になっていると思うのですが\" 関数形を解析的に書けないように思います。 パラメータの値を具体的に与えたうえでシミュレーションして確率を求める方針をとることはできます。",
"課題か何かでしょうか。実務的にはほとんど意味がない計算にしかならないと思います(構成要素の網羅度が足りなさすぎる、ある程度網羅したら複雑すぎて計算は困難)"
] | 2 |
Technology
| 0 |
499
|
retrocomputing
|
Plessey computer at Stanford?
|
While updating the wiki article on the 4004, I came across an interesting claim by Ted Hoff, who stated the idea of using a general-purpose CPU in a calculator came to him due to a minicomputer that had been donated to Stanford by the UK company Plessey.
I'm at a loss as to what this might be... I know Plessey had a range of realtime machines used for telephone exchanges and the Linesman radar system (rather unsuccessfully) but these were mainframe sized and I cannot find a hint of a mini.
I suppose this could be any old mini that Plessey bought and donated, but it seems less likely that Hoff would refer to it that way, if AT&T donated a PDP-11 to Stanford someone talking about it later would likely refer to it as "a dec mini".
|
https://retrocomputing.stackexchange.com/questions/24545/plessey-computer-at-stanford
|
[
"minicomputers"
] | 9 | 2022-05-23T09:04:36 |
[
"On the face of it, the dates don't work, but 1. the information in Wikipeda is not sourced 2. a prototype might have been given to a university before it was ready for sale - perhaps hardware would have been available before suitable software was written.",
"@mikado - had not heard of this - a little late for the timeline but an interesting device... and apparently actually used in the 90s!",
"en.wikipedia.org/wiki/Plessey_System_250?wprov=sfla1 sounds like an interesting and unusual system",
"Whatever it was, it needs to have been in Stanford in 1969, to fit the 4004 narrative.",
"forum.stanford.edu/wiki/index.php/…. has no indication of a Plessey as one of the early computers at Stanford. Doesn't rule it out though...",
"@another-dave Right. At least that's the only one I know. In fact, I've seen one not long ago at the VCL collection in Neubiberg.",
"Per Wikipedia, Plessey was in the PDP-11-compatible business. But that might be a little late for 4004 work."
] | 7 |
Technology
| 0 |
500
|
retrocomputing
|
Looking for late 90s shareware open world racing game
|
I'm trying to track down a shareware racing game released somewhere between 1999 and 2004 - or at least, my parents found it bundled in a computer magazine during that time.
Here's what I remember about it:
* It was a Win9x game, 3D Flat shaded with hard edges and basically no textures, no actual transparency and rather sparse geometry; It wasn't due to low settings, it was just stylized like that;
* It was open world;
* The scope of the game was basically collecting (pinkish?) waypoints randomly placed around the map within a time limit;
* It was probably made by an European dev;
* the "buy the game" screen showed a few other maps, including a "rainbows in the sky" fantasy setting.
It seems that most websites curating shareware games have just disappeared from the face of the earth, so I haven't found any reference about it online.
Does my description ring any bells to anyone?
|
https://retrocomputing.stackexchange.com/questions/21755/looking-for-late-90s-shareware-open-world-racing-game
|
[
"identify-this-game"
] | 9 | 2021-09-09T01:58:28 |
[
"Are you really sure that it is a Win9x game? Low Poly graphics without texturing could also mean, that it was a DOS game.",
"@thkala you were absolutely alone against time, and the car in the demo was just one extremely low poly sedan. The physics and handling weren’t too arcades, but very far from current day realism level.",
"Do you remember anything about the cars? Were they street cars? F1-type? Off-road vehicles? Were you alone against time, or were there NPCs?",
"I wish I could give some more details but there's very little to add. I mean, I thought it was popular enough given it was deemed worthy of being bundled on a magazine. I'll check it out on discord.",
"Since I see there's one close vote, I won't wait to mention that, if you don't get an answer here, try /r/TipOfMyJoystick or the #identify-a-game channel on the MobyGames Discord.",
"An italian magazine by Future Media called \"Giochi per il mio computer\" which was the local edition of \"PC Gamer\". I've already tried browsing archive.org for some clues but couldn't find anything.",
"Can you remember which magazine it might have been ?",
"Nope, it was clearly a small team or one-man made game. Much more lo-fi than the Interstate games.",
"Interstate 76 or Interstate 82 ?"
] | 9 |
Technology
| 0 |
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