Error java.lang.OutOfMemoryError: PermGen space
java.lang.OutOfMemoryError: PermGen space Exception
Evaluating the sum $\sum_{n=1}^{\infty}\dfrac{(-1)^{n}}{n^{2}}$ I am tasked to evaluate the sum  $$\sum_{n=1}^{\infty}\dfrac{(-1)^{n}}{n^{2}}$$ Using contour integration. This is what I've done so far.   Let $C_{N}$ be the square defined by the lines $x=\pm(N+\tfrac{1}{2})\pi$ and $y=\pm(N+\tfrac{1}{2})\pi$. Let $f=\tfrac{1}{z^{2}\sin(z)}$. I was able to prove that  $$\int_{C_{N}}\dfrac{1}{z^{2}\sin(z)}dz=2\pi i\left[\dfrac{1}{6}+2\sum_{n=1}^{N}\dfrac{(-1)^{n}}{\pi^{2}n^{2}} \right]. $$  By Cauchy's residue theorem. So now if I could prove that he integral converges to zero then I would be done. The problem is that I can't seem to get an upper bound on the integral. I've having trouble with the fact that $|f|$ is unbounded within $C_{N}$ so ML inequality doesn't help me. Any hints would be great. Thanks. How do you switch from Wayland back to Xorg in Ubuntu 17.10? Some of my applications don't work on Ubuntu 17.10 Wayland. How can I switch back to Xorg? Why does the new review page sometimes shows questions to vote to close without anybody having voted to close it? Does herd behavior influence the SO sites? Are you influenced by existing votes? That is, if a question or answer has a large number of up votes, are you more likely to vote it up (and similar for down)?  The reason I'm putting this question is this: on these sites we see how other people vote before we do. This almost certainly influences us (see resources, below) - just as we can be influenced by our  (people often naturally pick the busy one).  This trend may also be further influenced by rep - do we give more weight to the answer of someone with 10K rep than someone with 10 - even if they both have e.g. zero votes?  And if this does happen, is it even a problem?  I'm not looking here for solutions - right now I'm just curious as to whether this is something you recognise.  Clarification edit: I'm referring to voting here. Example: if you see a question or answer with 20 plus votes, are you more likely to vote it up than if it has no votes, or a negative number vote?  Bounty: I've been so impressed at the quality of answers and comments here that I'm offering a small bounty to encourage more great responses and discussion.  Wrapped up: Bounty awarded to the answer that received the most votes. In light of the question, it only seemed appropriate...  Resources: $ \frac{1}{a^{2} + b^{2} + 1} + \frac{1}{b^{2}+c^{2}+1} + \frac{1}{c^{2} + a^{2} + 1} \ge 1 $, prove $ab + bc + ca \le 3$ If $a,b,c$ real numbers such that $$ \frac{1}{a^{2} + b^{2} + 1} + \frac{1}{b^{2}+c^{2}+1} + \frac{1}{c^{2} + a^{2} + 1} \ge 1 $$,  prove that $ab + bc + ca \le 3$.     Attempt:  Assume that $a,b,c &gt; 0$.   $$ \frac{1}{a^{2} + b^{2} + 1} + \frac{1}{b^{2}+c^{2}+1} + \frac{1}{c^{2} + a^{2} + 1} \ge 1  $$ $$ \implies  (a^{2} + b^{2} + 1)(b^{2}+c^{2}+1) + (a^{2} + b^{2} + 1)(a^{2}+c^{2}+1) +  (a^{2} + c^{2} + 1)(b^{2}+c^{2}+1) \ge (a^{2} + b^{2} + 1)(b^{2}+c^{2}+1)(c^{2} + a^{2} + 1)$$  $$ \implies  ((ab)^{2} + (ac)^{2} + (bc)^{2} + a^{2} + 2 b^{2} + c^{2} + b^{4} + 1) + ((ab)^{2} + (ac)^{2} + (bc)^{2} + b^{2} + 2 a^{2} + c^{2} + a^{4} + 1) + ((ab)^{2} + (ac)^{2} + (bc)^{2} + a^{2} + 2 c^{2} + b^{2} + c^{4} + 1) \ge (a^{2} + b^{2} + 1)(b^{2}+c^{2}+1)(c^{2} + a^{2} + 1)$$  $$ \implies  3((ab)^{2} + (ac)^{2} + (bc)^{2}) + 4(a^{2} + b^{2} + c^{2}) + (a^{4}+b^{4}+c^{4}) + 3  \ge (a^{2} + b^{2} + 1)(b^{2}+c^{2}+1)(c^{2} + a^{2} + 1)$$  Next, notice  $$(a^{2} + b^{2} + 1)(b^{2}+c^{2}+1)(c^{2} + a^{2} + 1) = ((ab)^{2} + (ac)^{2} + (bc)^{2} + a^{2} + 2 b^{2} + c^{2} + b^{4} + 1)(c^{2} + a^{2} + 1) $$ $$ = (abc)^{2} + a^{2}c^{4} + b^{2}c^{4} + (ac)^{2} + 2(bc)^{2} + c^{4} + b^{4}c^{2} + c^{2} + a^{4} b^{2} + a^{4}c^{2} + (abc)^{2} + a^{4}  + 2(ab)^{2} + (ac)^{2} + b^{4}a^{2} + a^{2} +  (ab)^{2} + (ac)^{2} + (bc)^{2} + a^{2} + 2 b^{2} + c^{2} + b^{4} + 1 $$ $$ = 2(abc)^{2} + 3(ac)^{2} + 3(bc)^{2} + 3(ab)^{2} + c^{4}a^{2} + c^{4} b^{2} + b^{4}a^{2} + b^{4} c^{2} + a^{4}b^{2} + a^{4} c^{2} + a^{4} + b^{4} + c^{4} + 2(a^{2} + b^{2} + c^{2}) + 1  $$  So we have  $$ \frac{1}{a^{2} + b^{2} + 1} + \frac{1}{b^{2}+c^{2}+1} + \frac{1}{c^{2} + a^{2} + 1} \ge 1 $$ $$ \implies  2(a^{2} + b^{2} + c^{2}) +  3  \ge 2(abc)^{2}  + c^{4}a^{2} + c^{4} b^{2} + b^{4}a^{2} + b^{4} c^{2} + a^{4}b^{2} + a^{4} c^{2} + 1 $$ Why is there such a big difference between "Size" and "Size on disk"? How to run grep and show x number of lines before and after the match grep returns just the line where it matched the regex and often what I want to really see is a few (say 2) lines above and below the matched one. Is there a simple way to achieve it?  EDIT: OS: Ubuntu based Bodhi Linux.  As mentioned in comments, -C does not work in vanilla but its GNU grep in my case. While using the Pixel Inspector, whenever I click "copy all values" it only copies values that you can see on the screen. Anyone know a solution? I need all the values to count the number of times 1, 2, and 0 appear on the graph. Links being changed to cppreference.com Someone just edited a link in one of my answers to point to a 'better reference'.    I've no problem with links being changed in general, but this smells like part of a concerted attempt to redirect traffic.   Is this kind of activity acceptable on SO? Is there actually a 0 probability of finding an electron in an orbital node? I've been using Ubuntu for a few years now, but I just installed Version 16.04, and I've been having a lot of issues. I'm not a command line expert, but I tried to install some software last night, and it is creating issues (and also not working properly).   When I run sudo apt-get -f install, I see the following message:  Reading package lists... Done Building dependency tree        Reading state information... Done Correcting dependencies... Done The following additional packages will be installed:   lua-event lua-expat lua-filesystem lua-sec lua-socket lua5.1 prosody Suggested packages:   lua-zlib lua-dbi-postgresql lua-dbi-mysql lua-dbi-sqlite3 The following packages will be REMOVED:   jitsi-meet-tokens The following NEW packages will be installed:   lua-event lua-expat lua-filesystem lua-sec lua-socket lua5.1 prosody 0 upgraded, 7 newly installed, 1 to remove and 22 not upgraded. 3 not fully installed or removed. Need to get 0 B/413 kB of archives. After this operation, 2,296 kB of additional disk space will be used. Do you want to continue? [Y/n] Y (Reading database ... 176266 files and directories currently installed.) Removing jitsi-meet-tokens (1.0.962-1) ... dpkg: error processing package jitsi-meet-tokens (--remove):  subprocess installed post-removal script returned error exit status 10 Errors were encountered while processing:  jitsi-meet-tokens E: Sub-process /usr/bin/dpkg returned an error code (1)   Can someone help me figure out what I need to do to get this resolved? I'm fine with deleting jitsi, but I'm not sure if that will correct the problem.   Currently there is a red circle with a line through it in the upper right corner that indicates there may be installed packages with unmet dependencies. I have a small question regarding using sudo with output redirect &gt;. To enable IP forwrding, someone can use the command:  echo 1 &gt; /proc/sys/net/ipv4/ip_forward   Executing this command will give permission denied as it requires root privileges. However, executing the same command with sudo gives also permission denied error! It seems that output redirect &gt; does not inherit the permissions of the preceding command echo. Is this right?  As a workaround I do:  echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward   Is this the best way to do it? Am I missing something?  Please, note that this is an example and it applies to all commands that use output redirect. How can I know if my macbook is hacked? Sleeping in a batch file When writing a batch file to automate something on a Windows box, I've needed to pause its execution for several seconds (usually in a test/wait loop, waiting for a process to start). At the time, the best solution I could find uses ping (I kid you not) to achieve the desired effect. I've found a better write-up of it , which describes a callable "wait.bat", implemented as follows:  @ping 127.0.0.1 -n 2 -w 1000 &gt; nul @ping 127.0.0.1 -n %1% -w 1000&gt; nul   You can then include calls to wait.bat in your own batch file, passing in the number of seconds to sleep.   (at last!). In the meantime, for those of us still using Windows&nbsp;XP, Windows 2000 or (sadly) , is there a better way?  I modified the sleep.py script in the , so that it defaults to one second if no arguments are passed on the command line:  import time, sys  time.sleep(float(sys.argv[1]) if len(sys.argv) &gt; 1 else 1) Footnote, non-inline syntax? I would like to use footnotes without cluttering the container paragraph. Something like:  This is a very long complex\footnote[a] sentence.  \foottext[a]{So complex that I would prefer to pull out the footnote text.}   The idea comes from the [linktext][1], [1]: http://url.com markdown syntax. For some reason, when I try to run any programs (I am trying to run a rootkit hunter: rkhunter) as root on the command line with sudo like this:  sudo rkhunter   Then I get this message:  You must be the root user to run this program   and then I get these lines:  sudo: error in /etc/sudo.conf, line 0 while loading plugin 'sudoers_policy' sudo: /usr/lib/sudo/sudoers.so must only be writable by owner sudo: fatal error, unable to load plugins   I try typing in just sudo but that comes up with the same three errors as above. Also in /etc/ sudo.conf does not exist.  I cannot run any other programs as root through sudo. It was also strange because I could run as root a day ago. I would like it to work.  Just so you know, I am the only user of this computer, and the administrator, running Lubuntu 14.04.1. LaTeX errors in Formatting I want to print this text :  make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg  But I feel because of the underscore , LaTeX generates an error missing $ inserted and it doesn't print it as well.  Secondly, In the \fbox{} , I wanted to print the two texts on the next line(i.e) one text per line , so I used \ and even \par but it doesn't seem to work and I would like to align the (or) as well.   \fbox{\texttt{uname -a}\\(or) \texttt{cat /proc/version}}   Here is my full source code:  \documentclass[12pt]{article} \author{Subham Soni S.} \date{\today} \title{Compiling and Installing a Kernel 3.13.3 On Ubuntu, Debian and its Derivatives} \begin{document} \maketitle To replace the existing \textsl{kernel} with a new one, do the following: \begin{enumerate} \item Create a folder named \emph{kernel} in the home directory. \item Download the latest kernel to the folder from  \texttt{www.kernel.org}. \item Extract the file. \item In the terminal, type the following command to \textbf{install the neccesary tools to compile the kernel}:   \begin{center}     \fbox{\texttt{sudo apt-get install gcc libncurses5-dev dpkg-dev}}   \end{center} \item Enter the directory of the extracted kernel source   \begin{center}     \fbox{\texttt{cd kernel} \par \texttt{cd linux-3.13.3}}   \end{center} \item Configure the kernel   \begin{center}     \fbox{\texttt{make menuconfig}}   \end{center}   In this menu you can customize your kernel \item Save and exit \item Compile the kernel   \begin{center}     \fbox{\texttt{make -j 5 KDEB_PKGVERSION=1.yourcustomname deb-pkg}}   \end{center}   \emph{This process might take a while...} \item Install the kernel   \begin{center}     \fbox{\texttt{sudo dpkg -i ../linux*.deb}}   \end{center} \item Reboot   \begin{center}     \fbox{\texttt{sudo reboot}}   \end{center} \item Run the following commands to check the kernel version   \begin{center}     \fbox{\texttt{uname -a}\\(or) \texttt{cat /proc/version}}   \end{center} \item You can easily uninstall the kernel with the command:   \begin{center}     \fbox{\texttt{sudo apt-get purge linux-image-3.13.3 linux-image-3.13.3-dbg}}   \end{center} \end{enumerate} \end{document} What is the exact difference between fluid and responsive design? Today I updated to version 2.18.52 &amp; I can’t see the names of the people who send me a message. The only thing I see is the WhatsApp logo and the word “message”.    I can’t also see the status my friends posts, they all look black. I uninstalled the app, reset my phone &amp; nothing seems to work so far. What is a serialVersionUID and why should I use it? Eclipse issues warnings when a serialVersionUID is missing.       The serializable class Foo does not declare a static final   serialVersionUID field of type long   What is serialVersionUID and why is it important?  Please show an example where missing serialVersionUID will cause a problem.