I am new to Networking and Databases, but im trying to learn MySQL and HTTP Requests to create a user Login for a game.  My goal is to let users create accounts and login to them etc (for Highscores etc). I discovered the Libgdx Net Module and also got my server running with MySQL, Apache and PHP.  I want to use php files to communicate with the Database on the Server.  But my question is (since there is not a big documention for libgdx Network Module):  Where and how can i learn how to create proper HTTP Requests in LibGDX and should i use JSON?   Just give me a hint how to start.  Thanks ;)
Backstory: I've been developing a game with LibGDX for the past two years, and I've seen it refactored more times than I remember.  I jumped on the iOS iKVM port as soon as it was released. But I've been struggling with it ever since in regards to cross platform networking.  Kryonet will not port over to iOS unfortunately. So it's either I ditch Kryonet, or lose a large chunk of my target audience (iOS Users)  My question for you is:  I noticed LibGDX has cross platform classes ready for sockets and HTTP Requests, but no documentation exists for these sockets at all.  Has anyone used these sockets at all in the past, and does anyone know how they work?
How to save an alias of an eval $(other_comand) command I've been using docker for a while and there's a command I write each time I boot up my docker:  eval $(docker-machine env)   I know eval shouldn't be used unless necessary, but it's mentioned by the following:  docker-machine env outputs environment variables like this:  docker-machine env export DOCKER_TLS_VERIFY="1" export DOCKER_HOST="tcp://&lt;some_ip&gt;:&lt;some_port&gt;" export DOCKER_CERT_PATH="/home/gableroux/.docker/machine/machines/default" export DOCKER_MACHINE_NAME="default" # Run this command to configure your shell:  # eval $(docker-machine env)   eval grabs these and load them in my current session.  Now what if I'd like to have an alias like this:  alias dockereval="eval $(docker-machine env)"   Syntax is good, but the problem is when a dotfile (let's say .zshrc as an example), well the content of the $() is evaluated when registering the alias when you source that file.  which dockereval   Results in  dockerenv: aliased to eval   I tried a few things like:  alias dockereval="docker-machine env | eval" alias dockereval="docker-machine env | /bin/bash" alias dockereval="eval `docker-machine env`"   but none did work. 2nd one is probably because it's running in a different session, 3rd does the same as $() I guess  Is there an other way to load these environment variables with an alias? Proving convergence of sums: If $\sum_{n=1}^{\infty}a^2_n$ and $\sum_{n=1}^{\infty}b^2_n$ converge then $\sum_{n=1}^{\infty}a_nb_n$ converges I am trying to solve this exercise from Royden's 3rd edition.     The question is as follows: Let $f$ be a real-valued function defined for all real numbers. Show that the set of points at which $f$ is continuous is a $G_{\delta}$.    Let $$A_n = \{y : \text{there is a }~\delta_y \gt 0 : |f(s)-f(t)|\lt 1/n ~ \text{whenever}~ s,t \in (y-\delta, y+\delta)\}\;.$$     Then by the definition of open sets, $A_n$ is open.     To complete the proof, I need help in showing that $f$ is continuous at say $x$ if and only if $x\in \cap A_n$.     If $f$ is continuous at $x$, the there is a $\delta \gt 0$ such that $|f(x) - f(a)| \lt 1/n$ whenever, $x\in (a-\delta, a+\delta)$. so $x \in A_n$ son it must be in $\cap A_n$.  Thanks. Using the Well Ordering Principle to Show that n^3 - n is divisible by 6. I read the following two sources and I think I understand the structure of proofs involving WOP, but I am stuck on the open-ended part where you prove P(n-1) for the  following problem:    Use the well-ordering principle to show that n^3 - n is divisible by 6.    Any help would be greatly appreciated!   Note: After factoring out (n-1)^3 - (n-1) it took the form of n^3 - 3n^2 + 2n and the only difference between that and n^3 - n is "3n^2 - 3n" which I proved was divisible by 6 via induction. Is there a better way to solve this problem?  Edit: , post is useful however I not supposed to use induction for the main part of the proof. First, when I never had installed sl:  diogosaraiva@Ubuntu:~$ sl O programa 'sl' não está instalado actualmente. Pode instalá-lo escrevendo: sudo apt-get install sl   traslaction: "The program 'sl' is not currently installed. You can install it by typing:"  But when I'm tired of it and I remove it by typing sudo apt-get remove sl per example...  I get this when I type sl:  -bash: /usr/games/sl: Ficheiro ou directoria inexistente   translate: "-bash: /usr/games/sl: No such file or directory" instead of:    diogosaraiva@Ubuntu:~$ sl O programa 'sl' não está instalado actualmente. Pode instalá-lo escrevendo: sudo apt-get install sl   This appears with others packages too...  How I get rid of this: -bash: /usr/games/sl: Ficheiro ou directoria inexistente ?  I want see the original:  diogosaraiva@Ubuntu:~$ sl O programa 'sl' não está instalado actualmente. Pode instalá-lo escrevendo: sudo apt-get install sl   Output of type sl  sl está hasheado (/usr/games/sl) Finding centrelines from polygons in QGIS? I was wondering if there is a way to create centre lines from polygons in QGIS? I have a polygon layer, but ideally need the centrelines as a separate file. CSS customized scroll bar in div Secure hash and salt for PHP passwords It is currently said that MD5 is partially unsafe. Taking this into consideration, I'd like to know which mechanism to use for password protection.  This question,   suggests that hashing multiple times may be a good idea, whereas  suggests using salt.  I'm using PHP. I want a safe and fast password encryption system. Hashing a password a million times may be safer, but also slower. How to achieve a good balance between speed and safety? Also, I'd prefer the result to have a constant number of characters.   The hashing mechanism must be available in PHP It must be safe It can use salt (in this case, are all salts equally good? Is there any way to generate good salts?)   Also, should I store two fields in the database (one using MD5 and another one using SHA, for example)? Would it make it safer or unsafer?  In case I wasn't clear enough, I want to know which hashing function(s) to use and how to pick a good salt in order to have a safe and fast password protection mechanism.  Related questions that don't quite cover my question: Prove that you can make change for any amount greater than 7 cents using only 3 and 5 cent coins. I am pretty sure this question has something to do with the Least Common Multiple.    I was thinking that the proof was that every number either is or isn't a multiple of $3, 5$, and $8\left(3 + 5\right)$. If it isn't a multiple of $3,5$, or $8$, great. You have nothing to prove. But if it is divisible by one of them, I couldn't find a general proof that showed that it wouldn't be divisible by another one. Say $15$, it is divisible by $3$ and $5$, but not $8$. Is adding a time dummy the same as estimating by within-time fixed effects? Sort sections according to alphabetical order Is it possible to tell latex, that it should sort the sections you used in your document according to their alphabetical order in the final pdf document? I.e. I want to have something like this  \begin{document} \section{A} \section{C} \section{B} \end{document}   and in the pdf I get the result as  A B C   Is that possible, and if yes, how? Putting the sections into separate files is not preferred (but possible if scripted) due to having ~300 sections. Edit: I can also rewrite it as   \begin{sortEnvironment}{Title} Content \end{sortEnvironment}   if that makes it easier. Non-pejorative synonym of "notoriety" I'm trying to say:       He probably gained some __________ [good notoriety] from this picture.   I was thinking publicity, but that connotes some kind of negative to me as well (like the stuff you see in gossip magazines at the checkout line).  I want a word as powerfully positive as notoriety is powerfully negative. How do moving charges produce magnetic fields? I'm tutoring high school students. I've always taught them that:     A charged particle moving without acceleration produces an electric as well as a magnetic field.   It produces an electric field because it's a charge particle. But when it is at rest, it doesn't produce a magnetic field. All of a sudden when it starts moving, it starts producing a magnetic field. Why? What happens to it when it starts moving? What makes it produce a magnetic field when it starts moving? which vectors are perpendicular to each other?  $\vec a = (1, -2, 3)$, $\vec b = (5, 4, 1)$, $\vec c = (1, 0, -5)$  Do i just take the dot product of 2 of them. If the dot product they are at $90^\circ$? But how do i know if there perpendicular? What special characters must be escaped in regular expressions? I am tired of always trying to guess, if I should escape special characters like '()[]{}|' etc. when using many implementations of regexps.  It is different with, for example, Python, sed, grep, awk, Perl, rename, Apache, find and so on. Is there any rule set which tells when I should, and when I should not, escape special characters? Does it depend on the regexp type, like PCRE, POSIX or extended regexps? I'm answering a question with a suggestion to use rename, and I realize I don't know what package it comes from (as part of the answer, I imagine saying something like "if you don't have rename, it's installed as part of [package]").  man rename tells me to SEE ALSO: mv(1), perl(1) - so my first thought is that it was installed with perl.  A related answer, , helps me figure out that the perl package includes prename but not rename - and it turns out that my /usr/bin/rename points to /etc/alternatives/rename which points to /usr/bin/prename  So this is still kind of confusing.  Did /etc/alternatives/rename point somewhere else before I installed perl?  Is there a general way to tell which package something comes from? I am using a logit model. My dependent variable is binary. However I have an independent variable which is categorical and contains the responses: 1.very good, 2.good, 3.average, 4.poor and 5.very poor. So, it is ordinal ("quantitative categorical"). I am not sure how to handle this in the model. I am using gretl.  [Note from @ttnphns: Although the question says the model is logit (because the dependent is categorical), the crucial issue - ordinal independent variables - is basically alike, be the dependent categorical or quantitative. Therefore the question is equally relevant to, say, linear regression too - as it is to logistic regression or other logit model.] My online friend is asking for money in order to visit my home country. Is this a legit request or a scam? On Travel.SE we often see questions about a person (usually a love interest) asking for money to pay for airfare, visas, permits and other expenses. For example        What general advice can be given in such situations to the person asking the question? Is it all a scam or can there be legitimate situations in which an online friend could be asking for money? I am in the last year of MSc. and would like to read string theory. I have the Zwiebach Book, but along with it what other advanced book can be followed, which can be a complimentary to Zwiebach. I would like a more mathematically rigorous book or lecture notes along with Zwiebach.   Specifically, mention whether the book discusses string theory   Rigorously? Intuitively?   What's the scope of the book? Does it cover the advanced materials, e.g. Matrix string theory, F-theory, string field theory, etc. Maybe even String Phenomenology? $$(1+2+\cdots+n)^2=1^3+2^3+\cdots+n^3$$  I noticed this only because $\displaystyle \sum_{i=1}^n i = \frac{n(n+1)}{2}$ and $\displaystyle \sum_{i=1}^n i^3 = \frac{n^2(n+1)^2}{4}$.  But the two things look completely different and I can't think of an intuitive reason I would have seen this connection. Something like the 'Proof Without Words' images. Or a trick I could use while expanding the right hand side to transform it to the sum of cubes.