What different between [[0] * n for i in range(n)] and [[0] * n] * n]  I have this code:  def matrix_decomposition(a):     n = len(a)     b = [[0] * n for i in range(n)]     c = [[0] * n for i in range(n)]     for j in range(0, n):         b[j][0] = a[j][0]         c[0][j] = a[0][j]/b[0][0]     for i in range(1, n):         for j in range(1, i+1):             b[i][j] = a[i][j] - sum(b[i][k]*c[k][j] for k in range(0, i))         for j in range(i, n):             c[i][j] = (a[i][j] - sum(b[i][k]*c[k][j] for k in range(0, i))) / b[i][i]     return b, c   and if I replace [[0] * n for i in range(n)] on [[0] * n] * n I get this error:     Traceback (most recent call last): File   "C:/Users/Noctus/PycharmProjects/lab3/matrix.py", line 46, in    [7, 22, 70, 149] File   "C:/Users/Noctus/PycharmProjects/lab3/matrix.py", line 27, in   matrix_decomposition c[i][j] = (a[i][j] - sum(b[i][k]*c[k][j] for k in   range(0, i))) / b[i][i] ZeroDivisionError: float division by zero   in 46 line I have:  b, c = matrix_decomposition([         [1, 2, 3, 4],         [2, 7, 21, 26],         [4, 13, 43, 88],         [7, 22, 70, 149] ])
I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?
What's the physical meaning of the imaginary component of impedance? As you know, impedance is defined as a complex number.  Ideal capacitors: $$ \frac {1} {j \omega C} \hspace{0.5 pc} \mathrm{or} \hspace{0.5 pc} \frac {1} {sC} $$  Ideal inductors: $$ j \omega L \hspace{0.5 pc} \mathrm{or} \hspace{0.5 pc} sL $$  I know that the reason why they 'invented' the concept of impedance is because it makes it easy to work with circuits in the frequency domain (or complex frequency domain).  However, since in real-life circuits both voltages and currents are real numbers, I'm wondering if there is any actual physical meaning behind the imaginary component of impedance. REST Service API executor.executeAsync Call Ends in Failure Function in Sharepoint Hosted App Any Answers Will Help me to Forward and Gain Knowledge in SharePoint Development  While i am Trying to get the list Items Using Rest API Calls in SharePoint Hosted App Using Below Function  function loadingSamples()  {     var JobListName = "RRR Jobs #";     var executor;     // Initialize the RequestExecutor with the app web URL.     executor = new SP.RequestExecutor("/");      //Fetching the choice values from the Job Status Field, to show in the Dropdown field     executor.executeAsync     ({         url: "/_api/web/lists/getbytitle('" + encodeURIComponent(JobListName) + "')/fields/getbytitle('Job Status')?$select=Choices",         method: "GET",         headers: { "Accept": "application/json; odata=verbose" },         success: successHandlerStatus,         error: errorHandler     }); } function successHandlerStatus(data)  {     alert("sucesss") }  function errorHandler(data, errorCode, errorMessage)  {     alert("errorMessage") }   It's always going to error function named errorHandler With  Error Code as -1002 and Error Message as Bad Request and Inside Data -> Body , the Error message is  {     "error":{            "code":"-1,Microsoft.SharePoint.Client.InvalidClientQueryException",         "message":{             "lang":"en-US",             "value":"The expression \"web/lists/getbytitle('DWR Jobs \" is not valid."         }     } }   Note :    This is working code in Sharepoint Hosted App that previously hosted in another Windows server. Now i hosted this App in New windows server,it's successfully hosted but it gives above mentioned Error in Rest Service Call. I'd like to build a version of Ubuntu that has absolutely no ability to recognize any USB device inserted. Is this possible?  There's the issue that mouses and keyboards nowadays are connected via usb, so I wonder if it's possible to recognize these but not everything else.  In the end it's a security measure, so different solutions to achieve this goal are also welcome. Is it possible to copy an object in Illustrator so that if you make a change in any of them the changes will apply in both? Actually I have this situation where I have a lot of instances of the same object and I need to be faster on changes and copy-ing again and again is not a proper solution, but consumes a lot fo time.  Thank you for your time! Discourage questions being marked as answered within an hour or so of being posted How do I preload a program for faster start? Is it possible to "preload"(actually not preload, but kinda emulate the startup) e.g. nautilus (or firefox) startup at login, so the first time I launch it myself it launches faster? Probably to start it on another desktop and close after some seconds? jQuery autocomplete tagging plug-in like StackOverflow's input tags? Tenure and tenure denial rates by universities Is there a way or website to find the tenure and tenure denial rates by universities and departments? I heard from some faculty that the tenure rate at X university is Y%, so I wonder if there is a way to find the statistics for all universities. "Since", "until", "from", "to" on invoices or date ranges of a form Which is the correct form on an invoice, or a general date range in a form, and why?  Monkey dolls                        12 GBP From 2012-01-03 to 2013-01-02  Monkey dolls                        12 GBP Since 2012-01-03 until 2013-01-02   Form format (dates can be modified with a datepicker):  Since: 2012-01-03 until: 2013-01-02   Since+until makes sense and sounds ok to me, yet I know I can be very wrong, at least when it comes to the common usage in the UK and/or US, since English is not my first language.  I am interested in both British and American English.  Until now I've been using since+until, yet some articles explicitly say they may not ever be used together, while some people and some other articles get deep into grammar rules which I can't really apply on the context of invoices and forms.  Here's a recent article saying since and until can never be used together (last paragraph):   Edit: The date range can start in the past or in the future, and can end in the past or in the future. However, at the time of issuing an invoice or rendering a form, you cannot know when the document will be read or how the form will be filled. How can we distribute Shamir's secret sharing scheme shares without a dealer? Let's say $k$ users have shares to a $(k,n)$ secret sharing scheme, and they want to issue new shares. How can they do this without collecting the shares together?  In particular, no set of $k-1$ users (including the new users) should be able to learn the shared secret during or after the share generating process. There is also no trusted third party.  One way to do this is by doing a secure multiparty computation. Is there a way to accomplish the task without a general multiparty computation scheme? Is the universe finite or infinite? Compute $\int_{0}^{\infty}\frac{x\sin 2x}{9+x^{2}} \, dx$ In the following code, I need to use +/- where I have used it, and plus/minus where I have used it.  \documentclass{amsart} \usepackage{lipsum} \usepackage{calc} \parindent=0 pt \parskip=12 pt plus 0 pt minus 0 pt \def\headsep{25pt} \newcommand{\LAYOUT}[5]{%   \setlength{\hoffset}{0pt}   \setlength{\voffset}{0pt}   \setlength{\topmargin}{#1 - 1in - \voffset - \headheight - \headsep}    \setlength{\oddsidemargin}{#2 - 1in - \hoffset}   \setlength{\evensidemargin}{\oddsidemargin}   \setlength{\textheight}{#3}   \setlength{\textwidth}{#4}   \setlength{\marginparwidth}{#5} } \newcommand{\FULLPAGE}{\LAYOUT{1in}{1in}{9in}{6.5in}{0.75in}}  \FULLPAGE \begin{document} \lipsum[1-10] \end{document}   If I replace the plus and minus in line 5 with + and - I get an enigmatic  "missing begin{document}" error.    If I replace the minus's in lines 10-11 with "-" I get an equally enigmatic error:  "Missing number, treated as zero. Illegal unit of measure (pt inserted)."   Can somebody please explain when one can use +/- and when one can use plus/minus?  Presumably there's a good reason why latex's error messages are so completely mystifying, and why inconsistencies like these keep appearing? It's really hard to explain to my coauthors, who regularly complain that latex is the most infuriating program ever devised by mankind.  Thanks very much for any advice!   Leo Storing output of command in shell variable What blueprints become available during story? As I progress, I realize that some blueprints open up throughout the story and don't have to be researched. Are these random or are they always the same and is there a list over those? Seems you can easily waste research point if you don't know that. Let $f\colon(0,\infty)\to\mathbb R$ be differentiable on $(0,\infty)$ and suppose that $\lim\limits_{x\to\infty} f'(x)=L$.         a. Show that for any $h&gt;0$, $\lim\limits_{x\to\infty} \frac{f(x+h)-f(x)}h=L$.      b. Show that $\lim\limits_{x\to\infty} \frac{f(x)} {x} =L$.   this is a differentiation question.  i don't know how to solve this question  Because it is Korean, it is difficult to deal with this cite. So for me, it is not easy to write.  thank you Semicolon or dash? How to make 7-zip do a whole bunch of folders A lady and a monster A famous problem:  A lady is in the center of the circular lake and a monster is on the boundary of the lake. The speed of the monster is $v_m$, and the speed of the swimming lady is $v_l$. The goal of the lady is to come to the ground without meeting the monster, and the goal of the monster is to meet the lady.  Under some conditions on $v_m,v_l$ the lady can always win. What if these conditions are not satisfied?  Edited: the monster cannot swim. If the conditions are not satisfied, then monster can always perform a strategy such that the lady will not escape the lake. On the other hand this strategy is not desirable for both of them because they do not reach their goals. As there was mentioned, this deals with undecidability of the problem. On the other hand, if you imagine yourself to be this lady/monster, you can be interested in the strategy which is not optimal. What is it? If there are such strategies in the game theory?  Edited2: My question is more general in fact. If we have a game with one parameter $v$ when two players $P_1, P_2$ are enemies and if $v&gt;0$ then for any strategy of $P_2$ the player $P_1$ wins. If $v\leq 0$ then for any strategy of $P_2$ there is a strategy of $P_1$ such that $P_2$ does not win and vice versa. I am interested in this case. From the mathematical point of view as I have understood the problem is undecidable since there is no an ultimate strategy neither for $P_1$ nor for $P_2$. But we are solving somehow these problem IRL. Imagine that you are a lady in this game - then you would like to win anyway even while knowing that your strategy can be covered by the strategy of the monster. On the other hand, the monster knows that if he will cover all strategies of the lady she will never reach the shore and he will never catch her. I mean they have to develop some non-optimal strategies. I hope now it's more clear. Additive function $T: \mathbb{R} \rightarrow \mathbb{R}$ that is not linear. A function $T:V \rightarrow W$ is additive if $T(x+y) = T(x) + T(y)$ for every $x, y \in V$. Prove that there exists an additive function $T: \mathbb{R} \rightarrow \mathbb{R}$ that is not linear.  My attempt: Let $T$ be the function $T: \mathbb{R}$ (over the field $\mathbb{Q}$) $\rightarrow \mathbb{R}$ (over the field $\mathbb{R}$). The set $\{1, \sqrt{2}\} \subseteq \mathbb{R}$ is linearly independent for the vector space $\mathbb{R}$ over $\mathbb{Q}$. Then, there must exist a linearly independent set $W \subseteq \mathbb{R}$ (over $\mathbb{Q}$) such that $\{1, \sqrt{2}\} \subseteq W \subseteq \text{span}(W) = \mathbb{R}$ (over $\mathbb{Q}$).  I have been told that the function defined as $T(1) = 1$ and $T(w) = 0$ for all $w \in \text{span}(W) \setminus \{1\}$ is additive but not linear, but I cannot see why this is? I can see why it is not linear, clearly $T(\sqrt{2} \cdot 1) = 0$ but $\sqrt{2} T(1) = \sqrt{2}$. But, why is $T$ additive? For example, $T(1+1) = T(2) =0$ but $T(1) + T(1) = 1+1 = 2$? Is there a mistake somewhere?