How to implode input's ids using jQuery?
Return matched elements' attribute ar array using jQuery
How do I change the default settings of export operators? How do you add tags to blocks so they can only be placed on 1 type of block? How do I install Waterfox? I estimated the sample covariance matrix $C$ of a sample and get a symmetric matrix. With $C$, I would like to create $n$-variate normal distributed r.n. but therefore I need the Cholesky decomposition of $C$. What should I do if $C$ is not positive definite? How to properly write multiple authors in bibtex file? I use  to store all articles I need and bibtex4word add-on (in MS Word) to maintain the reference list. So, I would like to know how to properly fill the "author" field in Jabref with multiple authors to appear them correct in the reference list.  For example, I've got the article with several authors:      E. Orti, J.L. Bredas, C. Clarisse   And I would like them to appear in this manner. But instead I get this:     C. C. E. Orti, J. L. Bredas Java: How to find if a method is overridden from base class? I need help!  I need to prove that for any $2 \le n,k$ positive integers $(n - 1)^2 \mid n^k -1$ if and only if $(n - 1) \mid k$  Thanks! Still alive, still alive after kill -9 / SIGKILL An apache2 process got stuck on my server and caused problems with other services. (original problem: kerneloops after USB hardware disconnect)   root@server:~# ps aux | grep apache2 | grep -v grep www-data 12917  0.0  0.1 412148 16156 ?        D    Jun27   0:00 /usr/sbin/apache2 -k start   Naturally, I killd it. it's still alive. so I kill -9d it. It's still "alive".  Now this is where the question gets serverfault/unix&amp;linux-worthy: Is there a way to get port 443 back without doing the obvious thing: rebooting? Iptables is installed.  Update: I could not resolve the Problem withouth rebooting. The general approach (use lsof or /proc/$PID/fd to find out which and get rid of that drive) as described here and in the "duplicate" could well have worked if not for additional (probably) hardware defects. Sum of Infinite Series $1 + 1/2 + 1/4 + 1/16 + \cdots$ Everyone knows about the classic  $$ \sum_{i=1}^{\infty} \dfrac{1}{2^i} = 1 $$ However, is there any way to find $$ \sum_{i=0}^{\infty} \dfrac{1}{2^{2^i}} = \dfrac12 + \dfrac14 + \dfrac{1}{16} + \dfrac{1}{256} + \cdots $$ Suppose I have something like the following:      \begin{eqnarray*} \mathrm{gcd}(x^3 + 6x^2 + 5x + 5, x^3 + 13x^2 + 6x + 3) &amp;=&amp; 102x^2 + 108x + 2 \ \mathrm{with} \ p = 109 \\ \mathrm{gcd}(x^3 + 2x^2 + 9x + 4, x^3 + 3x^2 + 7x + 9) &amp;=&amp; 1 \ \mathrm{with} \ p = 131 \\ \mathrm{gcd}(x^3 + 3x^2 + 9x + 12, x^3 + 6x^2 + 12x + 4) &amp;=&amp; 6x + 122 \ \mathrm{with} \ p = 157 \end{eqnarray*}   How do I align the statements at the end of each line (i.e. the "with p = ..." bit) to the right? How can I tell if two pictures were taken with the same camera without metadata? Is it possible to identify images (without exif data) and link them to the exact same camera? If so, I'd like some software recommendations to get the job done.  I have two photos that I'd like to compare whether they were taken with the same camera or not. They both seem to lack EXIF data but I am sure I've heard of other hidden fingerprints to be found within the images.  For instance, sensor noise should be rather consistent if the photos were taken with the same camera, pretty much like firing a handgun and the bullet gets unique marks. I've also heard that the camera manufacturers sometimes add a hidden watermark which can be read with some special software. Function representing a forest fire after one time step Show that if $fd'=f'd $ and the pairs $f, d $ and $f',d' $ are coprime, then $f=f' $ and $d=d' $. Show that if $fd'=f'd $ and the pair $f, d $ are coprime, that is gcd($d,f $)=1, as is the pair $f',d' $, then $f=f' $ and $d=d' $.  This should be simple, but I couldn't verify it. Thanks in advance! Limiting number of lines in textarea I'm looking for a javascript that can limit the number of lines (by line I mean some text ended by user pressing enter on the keyboard) the user is able to enter in textarea. I've found some solutions but they simply don't work or behave really weird. The best solution would be a jquery plugin that can do the work - something like , but it should be able to limit text line count not character count. The Java documentation says:      It is not possible for two invocations of synchronized methods on the   same object to interleave.   What does this mean for a static method?  Since a static method has no associated object, will the synchronized keyword lock on the class, instead of the object? OrderBy and OrderByDescending are stable? Show that $\mathbb{Q}\times \mathbb{Q}$ is denumerable I am new to functions and relations, and with some concepts I am not so familiar. I have a question in an homework:     Show that $\mathbb{Q} \times\mathbb{Q}$ is denumerable.   From what I understood, denumerable means that it is infinitively countable. There are some  on the web about this topic, but I am still not understanding their explanation, maybe because they are not explained so easily (for me).  From what I understood, a set is denumerable if there's a relation with the natural numbers (but I am still not understanding what is this relation).  I have heard also about equinumerous sets (contain a bijective function = onto + one-to-one function), but I cannot relate this information with the problem to try to solve it. Construct a command by putting a string into a tty I managed to do this  echo -n "command" &gt; /dev/tty1  The letters appear, and the cursor moves, but they are "ghosts" – if you hit Enter, nothing happens (they are not in stdin).  Edit:  In the middle of the below screenshot, you see why I see the use of this. (The line with a red caption, right below the line with a yellow caption.) As it is now, you are not really "editing" the note text; you are just asked to write a new text, which will replace the text of the note you are (not really) editing. Thus, I thought it could be remedied by simply pasting the old text into the tty: if the user hits enter, no modification is made. (This program is in Perl/MySQL, but I thought it would be more interesting to ask for a general solution than "how do I do this in Perl".)    Edit 2:  Here is the Perl code, that uses the C code below (works exactly as intended), as well as a new screenshot – hopefully this will clarify things beyond doubt :) Again, look at the middle of the screenshot, where the edit is made to the note text - this time around, the old text is there, for example if you just wanted to fix a typo, you won't have to retype the entire note text.  my $edit_note_text = $edit_note_data[2]; print BOLD, RED, " new text: ", RESET; system("writevt /dev/tty \"$edit_note_text\""); my $new_text = &lt;$in&gt;; $new_text = fix_input($new_text); my $set_text = "UPDATE notes SET note = \"$new_text\" WHERE id = $edit_note_id"; $db-&gt;do($set_text); If gravity isn't a force, then why do we learn in school that it is? Checking for a file and whether it is readable and writable I'm trying to write a script that will look for a certain .txt file saved to my desktop.  I want the script to be able to check if this file exists and then check to see if it is readable and writable.  Any hints?