Null Pointer exception
What is a NullPointerException, and how do I fix it?
Evaluate $\sum_{k=1}^\infty\frac{x^k}{k(k+1)}$ My partner is tutoring a Civil Engineering student in maths. Conveniently, I am a civil engineer so when any maths that's confusing comes up, I can usually help out. However, we are having a problem with the summing of power series, one area where I am sorely lacking.  After spending two hours on a question, we still cannot solve it and are always left with a $k$. Admittedly, I don't fully know what I am doing.     Evaluate $\displaystyle \sum_{k=1}^\infty\frac{x^k}{k(k+1)}$.   We do know that the answer is $1 + \dfrac{1-x}{x}\ln (1-x)$.  Any hints or help in the direction to go would be very much appreciated. Schengen Visa Refusal: Justification for the purpose and conditions of the intended stay was not reliable How does Windows know whether it has internet access or if a Wi-Fi connection requires in-browser authentication? R script line numbers at error? Set Xorg to use only part of the screen Interscholastic Mathematics League Senior B Division #2 Points $P$, $Q$, $R$ and $S$ are chosen on the sides of parallelogram $ABCD$, so that $P$ is on line $AB$, $Q$ is on line $BC$, $R$ is on line $CD$, $S$ is on line $DA$, and $AP=BQ=CR=DS=\frac{1}{3}(AB)$. Compute the ratio of the area of $PQRS$ to the area of $ABCD$. "There IS/ARE rice, meat and tomatoes on my plate" In Java, is there any way to use the JDK libraries to discover the private classes implemented within another class? Or do I need so use something like asm? Problem with glossary I am copying the very first piece of code from  in order to create a glossary. While I get no problem in the compilation I do not get the "glossary part" that appears in the example. I literally copy paste.  Also, I want to create a document that only consists of a glossary of various terms. That is to put everything in alphabetical order (with the possibility to include references as well). How could I possibly do this? I tried some itemize options with alphabetical order but does not look that good. How to resolve "iTunes could not back up the iPhone because the backup was corrupt"? When I try to sync my iPhone with my computer, I get the following message:       iTunes could not back up the iPhone "iPhone Name"   because the backup was corrupt or not compatible   with the iPhone.      Delete the backup for this iPhone, then try again.   Yet, here is no option to delete the backup. Where are backups stored / how can I delete the backup?  This is iTunes version 10.5.3 running under  Mac OS X 10.6.8. How can I get rid of this black hole in my minecraft world? I have interesting bug that I have experienced before but has gone away on its own. This one is not going away though.  I have a giant stripe or chunks missing from my desert biome, I would say probably 7 chunks long.  I'm guessing the chunks are corrupted or something, what was hoping to figure is whether it can repaired or reverted.  Here is a picture of the problem. How can I increase my Vault Dweller's Happiness? TeX capacity exceeded with glossary package My document contains many thousands of glossary items. When compiling with XeLaTeX, about 1/8 of the way through the document, it reports:  ! TeX capacity exceeded, sorry [main memory size=3000000]. \@glolist@ ...},{13586},{9406},{4539},{12811},{179                                                   51},{5831},{1047},{14948},    The numbers you see above are ones placed in #1 of \newglossaryentry{#1}{#2}. These unique numbers are assigned to each entry for convenience. I have successfully compiled short tests of the document, which only used 1% of the full content. The resulting .glo file is about 1 MB in size.   Could this be the result of some error on my part or am I giving TeX too much work to do?  Update:  I have followed the instructions below (edited texmf.cnf and running  fmtutil-sys --all. This has allowed me to compile an additional portion of the book, but no matter the settings I add, I can't go beyond 5/8 of the way through.  A compile with extra_mem_top.xelatex = 30000000 and extra_mem_top.xelatex = 50000000 both result in:  TeX capacity exceeded, sorry [pool size=3186676].   Update:  I have done the following:  $ kpsewhich texmf.cnf /usr/local/texlive/2011/texmf.cnf $ nano /usr/local/texlive/2011/texmf.cnf   To the texmf.cnf file, following instructions at , I added:  main_memory = 230000000 extra_mem_top = 10000000 extra_mem_bot = 10000000 save_size = 150000 stack_size = 150000  main_memory.xelatex = 30000000 extra_mem_top.xelatex = 30000000   After this, I tried: - fmtutil-sys --all, then compiling xelatex file.tex. - fmtutil --all, then compiling xelatex file.tex. - fmtutil-sys --byfmt xelatex, then compiling with xelatex file.tex. - texhash, then compiling with xelatex file.tex.  All of these resulted in no changes in results. I still get:  TeX capacity exceeded, sorry [pool size=3186676]. How does one go about proving that the function $x \sin x$ is not uniformly continuous on the set of real numbers ?  Any method that uses the sequential criterion for discontinuity would be preferred.  Thanks in advance ! Understanding the Basic Context of Trusted Hosts I got the trusted host settings error.      The trusted_host_patterns setting is not configured in settings.php. This can lead to security vulnerabilities. It is highly recommended that you configure this. See Protecting against HTTP HOST Header attacks for more information.    I read the  but I'm not understanding some of the basic context.   Are the "trusted hosts" me and other administrators who want to be able to administer the site remotely?  If so, would I add my PC's domain to the trusted host list? "Screaming" noise while steaming milk? Evaluate the limit      $$ \lim_{n\rightarrow \infty}\left(\frac{n+1}{n}\right)^{n^2}\cdot \frac{1}{e^n} $$   My Attempt:  $$ \lim_{n\rightarrow \infty}\left(\frac{n+1}{n}\right)^{n^2}\cdot \frac{1}{e^n} = \lim_{n\rightarrow \infty}\left(1+\frac{1}{n}\right)^{n^2}\cdot \frac{1}{e^n} $$  How can I solve the problem from this point? Piping STDERR vs. STDOUT According to "" (pg. 44), you can pipe only STDERR using the |&amp; redirection symbols.  I've written a pretty simple script to test this:  #!/bin/bash echo "Normal Text." echo "Error Text." &gt;&amp;2   I run this script like this:  ./script.sh |&amp; sed 's:^:\t:'   Presumably, only the lines printed to STDERR will be indented. However, it doesn't actually work like this, as I see:      Normal Text.     Error Text.    What am I doing wrong here? How to edit a file in vi editor (arrow keys prints letters)? I am open a file in vi:  vi index.php   Here the problem is: when I press the down arrow and it prints 'B'. Why it prints 'B'? How can I sync the new "people" (face recognition) metadata across devices in Photos (iOS 10 and MacOS Sierra)? The new Photos updates for iOS 10 and MacOS Sierra includes a much more powerful and integrated approach to organizing photos by who's in them.  It's built around powerful, on-device facial recognition.  But once it does its automated thing (finding the faces it thinks are the same person), there's still a lot of manual merging and labeling to be done if you have a lot of photos and are as obsessive about organization as I am.  For example, if you have, say... three thousand photos of your daughter, Photos will find almost all of them, but may guess they're 5 or 6 different people.  So you have to merge the buckets that all are one person, assign them a name (so you can search by it), etc.  But unlike other changes (edits, deletions, organization into albums, etc.), manual changes to "people" data don't seem to sync at all by default.      Is there really no way to do this?  It seems bizarre that one of the flagship features Apple's touting in this Photos update doesn't play at all with what was Photos primary selling point over iPhoto - everything synced on all your devices.