Embedding Javascript (file): what means "filename.js?v=2.0.4"?
Why pass parameters to CSS and JavaScript link files like src="../cnt.js?ver=4.0"?
When in many rooms, user's info goes off screen So, I wanted to check what low-number rooms are still active so I joined a bunch of rooms in the chat.  This is the result:    Bug also exists when expending rooms on the side:    Since the position is fixed I can't scroll down.  Proposed fix:  Only show the first 10 rooms, and show ... pointing to the user's profile for other rooms. Mysql strip time component from datetime I need to do a date comparison in Mysql without taking into account the time component i.e. i need to convert '2008-11-05 14:30:00' to '2008-11-05'  Currently i am doing this:  SELECT from_days(to_days(my_date))   Is there a proper way of doing this? Combinatorics - Painting the Unit Squares of a 3x3 Square I want to prove with mathematical induction that:  $$\sum_{i=1}^n i \cdot i! = (n+1)! - 1$$  So in the first step we define $n = 1$:  $$\sum_{i=1}^1 i \cdot i! = 1 \cdot 1! = 1 = 2! - 1$$  In the second step we define $n = n + 1$:  $$\sum_{i=1}^{n+1} i \cdot i! = \sum_{i=1}^n i \cdot i! + (n+1)(n+1)!$$ $$\implies (n+1)! - 1 + (n+1)(n+1)!$$  This can now be simplified to $(n+2)(n+1)! - 1$ but I do not see how...  We could do $(n+1)!(-1 + (n+1)) = (n+1)! \cdot n$ but still this will not be the same as above.  What did I miss?  Bodo Why are all nonzero eigenvalues of the skew-symmetric real matrices pure imaginary? Assume that $A$ is an $n\times n$  real matrix, i.e. $$A^T=-A.$$  Since $\det(A-\lambda I)=\det(A^T-\lambda I)$, $A$ and $A^T$ have the same eigenvalues. On the other hand, $A^T$ and $-A$ also have the same eigenvalues. Thus if $\lambda$ is an eigenvalue of $A$, so is $-\lambda$. If $n$ is odd, $\lambda = 0 $ is an eigenvalue.  A curious search in Google returns  the nonzero eigenvalues of $A$ are all pure imaginary and thus are of the form $iλ_1, −iλ_1, iλ_2, −iλ_2,$ … where each of the $λ_k$ are real.   Here is my question:     How can I prove the fact that "the nonzero eigenvalues of $A$ are all pure imaginary"? How can I run a DSLR from AC power? My wife has a Nikon D3100 that I've been using to film, but the battery typically won't last through long shoots.  I've gathered from searching around that I can't charge the camera with USB, but I wondered if there's ANY way to do that. It seems at least possible that an adapter could exist that would fill in for the battery and plug into the wall, but I haven't been able to find such a thing.  Is there such a product or technique? It would be nice to not buy a second battery, I'm really hoping for a "set it and forget it" solution. When ssh'ing, how can I set an environment variable on the server that changes from session to session? Does the  tag position in HTML affects performance of the webpage? What's the difference when using GET or POST method? Which one is more secure? What are (dis)advantages of each of them?  () Math mode accents In my long document I, sadly, have to use several accents to denote different kinds of symbols. Currently, I use primes ($x'$), hat, tilde, and overline. In addition I use two colored symbols (red colored tilde and blue $\prescript\ulcorner$), as I need further distinguishment.  Now I'd like to have no colors in my document, while I still have at least six different ways to differentiate certain symbols.  Which alternatives could I use that are easy to recognize and 'stand out', while they are different to prime/hat/tilde/overline?  EDIT: The reader should be able to see the kind of accent used even if the symbol in question is in a sub-script (possibly even a sub-sub-script). See , page 2: the internal logic diagram for the MM74HC138.    The diagram shows logic inverters with bubbles at the input or at the output. Is there an actual difference between them? For realism should I use the maximum number of Subsurf levels? I was wondering if I always need to use the maximum value of the options from the elements of "Add Modifier". For example, do I need to use the view 6 in Subdivision surface? I know it depends of what we are trying to achieve, but we all want the same. Make something look the most believable. So do you always use the maximum value Blender offers? Let $f(\sin x)$ be a given function of $\sin x$.   How would I show that $\int_0^\pi xf(\sin x)dx=\frac{1}{2}\pi\int_0^\pi f(\sin x)dx$? Drawing a 3D cylinder, and a circle shape on the x---y plane I'm trying to draw a cylinder on the three dimensional space, and I also want its projection on the x--y plane. I found the first answer  to be very useful. I just copy-paste it to my document, and modify it as follows (the modifications are only inside the \begin{tikzpicture} tags):   \documentclass[parskip]{scrartcl} \usepackage[margin=15mm]{geometry} \usepackage{tikz}  \pgfmathsetmacro{\xdeg}{30} \pgfmathsetmacro{\xx}{cos(\xdeg)} \pgfmathsetmacro{\xy}{sin(\xdeg)}  \pgfmathsetmacro{\ydeg}{120} \pgfmathsetmacro{\yx}{cos(\ydeg)} \pgfmathsetmacro{\yy}{sin(\ydeg)}  \pgfmathsetmacro{\zdeg}{80} \pgfmathsetmacro{\zx}{cos(\zdeg)} \pgfmathsetmacro{\zy}{sin(\zdeg)}  \newcommand{\tdcyl}[5]{% origin x, origin y, origin z, radius, height     \path (1,0,0);     \pgfgetlastxy{\cylxx}{\cylxy}     \path (0,1,0);     \pgfgetlastxy{\cylyx}{\cylyy}     \path (0,0,1);     \pgfgetlastxy{\cylzx}{\cylzy}     \pgfmathsetmacro{\cylt}{(\cylzy * \cylyx - \cylzx * \cylyy)/ (\cylzy * \cylxx - \cylzx * \cylxy)}     \pgfmathsetmacro{\ang}{atan(\cylt)}     \pgfmathsetmacro{\ct}{1/sqrt(1 + (\cylt)^2)}     \pgfmathsetmacro{\st}{\cylt * \ct}     \filldraw[fill=white] (#4*\ct+#1,#4*\st+#2,#3) -- ++(0,0,#5) arc[start angle=\ang,delta angle=-180,radius=#4] -- ++(0,0,-#5) arc[start angle=\ang+180,delta angle=180,radius=#4];     \filldraw[fill=white] (#1,#2,#3+#5) circle[radius=#4]; }       \begin{tikzpicture}[x={(\xx*1cm,\xy*1cm)},y={(\yx*1cm,\yy*1cm)},z={(\zx*1cm,\zy*1cm)}]          \tdcyl{-3}{-3}{0}{1}{3} % x y z   r h         \tdcyl{0}{0}{0}{1}{3} % x y z   r h           \draw (-3,0,0) -- (3,0,0) node[circle,fill=white] {x};         \draw (0,-3,0) -- (0,3,0) node[circle] {y};         \draw (0,0,-3) -- (0,0,3) node[circle] {z};     \end{tikzpicture}     \end{document}   I added another cylinder and tweaked the positions to fit what I need. This produces the following:      Which is almost what I want, except that I want to see the projection of that cylinder on the x--y plane, but unfortunately, the top cylinder hides the full circle. When I disable the top cylinder:      \begin{tikzpicture}[x={(\xx*1cm,\xy*1cm)},y={(\yx*1cm,\yy*1cm)},z={(\zx*1cm,\zy*1cm)}]          \tdcyl{-3}{-3}{0}{1}{3} % x y z   r h            \draw (-3,0,0) -- (3,0,0) node[circle,fill=white] {x};         \draw (0,-3,0) -- (0,3,0) node[circle] {y};         \draw (0,0,-3) -- (0,0,3) node[circle] {z};     \end{tikzpicture}   Now the projection is shown again:   But the top cylinder is missing...  How can I make the top cylinder transparent, or, alternatively, and even better; how do I create one long cylinder and emphasize its projection on the x--y plane?   BTW, what determines the position of the labels x,y,z in the above code? I want to reposition them so they won't overlap with the axis. Thanks in advanced! Are recommendation questions an acceptable kind of list-type question or should they be closed? Recommendations are a recurring topic on multiple Stack Exchange (SE) sites. Some sites allow recommendations (ex: ), some do not (ex: ). There are many reasons for that and I can still remember animated discussions on this subject on the Gaming meta. Then there is that existential problem with Sci-Fi SE, &quot;What problems does answering a question on this site solve?&quot;  The only common problem I can think of is What to read/watch next?, which obviously led to a big number of recommendation questions, later slightly disguised as list question. And the main trouble with these questions isn't objectivity at all, some of them aren't even subjective. It's the fact that they don't have an answer - they are open ended. -  Those questions are monstrously popular because:  There's an actual problem to be solved,  or  This problem is quite common.  In view of the  blog post, a recommendation question fails the &quot;real questions have answers, not items or ideas or opinions.&quot; criteria. But it's still a &quot;practical, answerable questions based on actual problems that you face. &quot; and it requires expertise to answer. The problem is that there are multiple acceptable answers, and the asker is not the best person to evaluate the best answer because he doesn't know which one is the best compared to the others, and he cannot test it in short term. Even the need to accept an answer is questionable. So, is a recommendation question an acceptable kind of list-type question or should it be closed just like any other list-type questions? Add existing ssh key for git Can't transfer purchases from iPhone to iTunes in iOS 9 After upgrading to iOS 9, I can't transfer purchases from my iPhone to iTunes. It happens to just start the process, then it finishes without transferring anything. However, I can still transfer purchases from my iPad with iOS 8.4 like before.   iPhone 5c, iOS 9 iTunes 12.3 MacBook Pro 13" with Retina Display Mid 2014, OS X El Capitan   Apparently, not many people happen to use this "transfer purchases" feature so it didn't get any real attention. I used it a lot, I used to update my apps on my iPhone, transfer them to iTunes and updated my iPad apps using iTunes. Still, I can update my apps using iTunes and update apps on all my devices. What happen if I install VirtualBox Guest Additions on a host? I have a bootable USB drive with Ubuntu installed.   This morning I Installed VirtualBox and booted my Ubuntu drive in a VM. I then installed the guest additions in Ubuntu.   My question/curiosity is, what would happen if I boot the drive again outside of the VirtualBox VM, using a physical computer?  Will my Ubuntu work normally or is something going to change? I've installed a version of Ubuntu Server and although I'm fairly still fresh with Ubuntu, I'm trying to create a bash file to run a program in the background. More importantly, I'm trying to get a file nameto display correct and create it before I start running the program (I like my debug stuff).  However, here is my bash script:    #!/bin/bash  PATH="/var/log/servers/Game/"  FILENAME="startup"  EXT=".log"  DATE=$(date +%d-%m-%Y)  NEWFILE=${PATH}${FILENAME}_${DATE}${EXT}   I have verified that the file does exist in the PATH directory. However, the issue is with the date command. When I run the script bash -x game.sh this is what is displays.   + PATH=/var/log/servers/Game/  + FILENAME=startup  + EXT=.log  ++ date +%d-%m-%Y  game.sh: line 5: date: command not found  + DATE=  + NEWFILE=/var/log/servers/Game/startup_.log  + echo /var/log/servers/Game/startup_.log   I don't understand why it would say the command doesn't work, when I can go to the main console and run date and get a valid response.  Any help is greatly appreciated! Is there a specific term for a statement that uses words such that their precise meaning conveys a subtext contrary to the colloquial meaning?  For example, the joke in Men in Black:     Gentlemen, congratulations. You're everything we've come to expect   from years of government training.   where the precise use of the words conveys a sarcastic meaning (ie that the candidates are inept because that's what he's come to expect from government training).  I was going to use "irony" to describe this but then realized this is basically the opposite of irony - the use of words to convey their literal intention, when a nonliteral intention was expected.