Getting error when I deploy WAR by IntelliJ
What is a NullPointerException, and how do I fix it?
Combining the second elements of a set of ordered pairs based on their first element How do I change the extension of multiple files? I would like to change a file extension from *.txt to *.text. I tried using the basename command, but I'm having trouble on changing more than one file.  Here's my code:  files=`ls -1 *.txt`  for x in $files do     mv $x "`basename $files .txt`.text" done   I'm getting this error:  basename: too many arguments Try basename --help' for more information I know classical physics, quantum mechanics, special relativity, and basic nuclear physics. I would like to get into some particle physics.   Where can I find a good introduction? It might be useful to segment books by whether they require quantum field theory or not. Self Teaching QFT I am currently in the process of teaching myself QFT.  It is not an easy task.  I have armed myself with many of the standard textbooks.  However, I am slow learner.   I get stuck on a thousand different terms which I don't understand, and a style of 'mathematics speak'  which loses me 95% of the time.   There are so many gaps in my knowledge that if I were a ship I would be at the bottom of the ocean.  What I really need is a book called 'QFT for Morons'. That's a bit harsh but 'QFT for dummies' doesn't quite express it clearly enough and besides there isn't such a book as far as I can find.  Any suggestions of resources or books that might help?   What I am really looking for is the one that explains QFT like you were talking to a five year old.  Perhaps I am asking the impossible.  I will add a bit more of a specific question here.    I have learnt that there are groups and non-abelian Lie groups like SU(2) etc., and then there a lagrangians, as well as a few other things like operators and states.   So a really dumb question is how are the lagrangians derived?  Are they determined by the group?  I am also confused because I understand some of the groups like SU(3) are used for different things in QFT.   I feel compelled to appologize for my ignorance but I am determined to make so more progress with this.   The problem when one is teaching oneself is you don't know which is the most fruitful path to follow. Let be $V$ a vector space over the complex numbers with inner product. Let be $T$ and $S$ linear operators in $V$ with adjoint operators $T^*$, and $S^*$ respectively. I know that it satisfies this: $\left&lt; T(x),y \right&gt;=\left&lt; x,T^{*}(y) \right&gt;$ $\left&lt; S(x),y \right&gt;=\left&lt; x,S^{*}(y) \right&gt;$    $\forall x,y \in V$ But, How can I prove that the adjoint operator of $ST$ is $(ST)^{*}$? And how can I  prove that $(ST)^{*}=T^{*}S^{*}$? How do I change the GRUB boot order? I have both Windows 7 and Ubuntu installed on a shared machine. Because a lot of the non-developers use Windows, I'd like to change the boot order to make it easier for them.  Currently the boot order looks like the following:   Ubuntu 11.10 kernelgeneric *86 Ubuntu 11.10 kernelgeneric *86 (safe boot)  Memory test Memory test Windows 7 on /dev/sda6   How do I change the default order so that Windows 7 is at the top of the list?   Windows 7 on /dev/sda6 Ubuntu 11.10 kernelgeneric *86 Ubuntu 11.10 kernelgeneric *86 (safe boot)  Memory test Memory test How do I find the length of an array? Android - How to change color of an ScrollView/ListView Overscroll?(see Desc. for example) How to write conditional equations with one-sided curly brackets As you are all most likely aware already all domain registrars ask for your personal information.   Such personal information includes:   Forename and surname Address information Email address Telephone number   Personal information via WHOIS  Depending on the domain type such as  or  this information may become immediately available after the registration of the domain via a simple whois. If you do not want that (and in most cases you certainly don't) they offer a service where you can remove this information from the whois service but of course hiding your personal information adds yearly costs to the domain  purchase.  What happens if I use fake details when registering a domain? Is "princessship" a real word? Are there any other words which have the same letter 3 times consecutively? Why is the decay of a neutral rho meson into two neutral pions forbidden? Was Stack Exchange named after Experts Exchange? Was Stack Exchange named after Experts Exchange, or is the former using the word "Exchange" a coincidence? What does the explicit keyword mean? For US federal tax, whether a taxpayer is subject to AMT is determined by a complicated way in Instructions for Form 1040, Line 45, which involves an incomprehensible "worksheet to see if you should fill in form 6251".  By simplification and approximation, is there a rule of thumb for an estimate of a salary value of a taxpayer, so that a salary above the value might cause the taxpayer to pay AMT with a big possibility, and a salary below the value might not with a big possibility?  Why do the following two sources seem to differ greatly in estimates of the boundary salary value:    says that  the possible boundary salary value for a single taxpayer  to pay AMT is $53,900.  says that      Taxpayers with small incomes fall within the AMT exemption limits.   That leaves the upper middle class to face the tax, especially those   with incomes between $200,000 and $500,000    Thanks. Too much space between full paragraph and subequations env I have a document using subequations and the parskip package. If the paragraph before a subequations environment is completely filled up to the last line, then additional vertical whitespace is introduced between this paragraph and the following subequations. I guess this is a bug, but I'm not sure, nor do I have enough TeX knowledge to try and fix it. How can I fix this whitespace issue?  Below is a MWE which shows the behaviour, at least on LaTeX2e &lt;2003/12/01> with pdfeTeX 3.141592-1.21a-2.2 (unfortunately on this machine only an old tetex distribution is installed).  \documentclass[a4paper,11pt]{article}  \usepackage{parskip} \usepackage{amsmath}  \begin{document}  The subequations environment provides a convenient way to number a foos \begin{subequations}\label{foo}   \begin{align}     x^2 + y^2 &amp;= z^2\\     a &amp;= b + c   \end{align} \end{subequations}  \end{document} What is the distance a creature or player can travel if they have multiple types of movement speeds? What is the distance a creature or player can travel if they have multiple types of movement?  For example, the  has a 40 ft walking speed, a 40 ft climbing speed, and an 80 ft flying speed. Can it move a total of 160 ft in a round using each of those fully, or is there another way this is calculated? How can I get numbered classes on rows? I worked briefly with Drupal 7 and I thought it was possible there but in Drupal 8 is it possible to have a view output an increasing numbered CSS classes for Views rows?  This is what I want.  &lt;div class="view"&gt;   &lt;div class="view-row-1"&gt;&lt;/div&gt;   &lt;div class="view-row-2"&gt;&lt;/div&gt;   &lt;div class="view-row-3"&gt;&lt;/div&gt;   &lt;div class="view-row-4"&gt;&lt;/div&gt; &lt;/div&gt;   I know I can add a CSS class to every row and give every row the same class. Fresh Windows-10 Install A Windows-7 laptop was upgraded to Windows-10 during the Microsoft free upgrade period when they were nudging users to migrate away from 7 to 10.  The system is sluggish and crash prone: I would like create a fresh install with a new SSD from a Windows 10 install .iso burned to a USB drive.  Is it possible (and how can) the the license-key from the old drive be recovered and migrated to a fresh install?   If this is not the right question to ask, I would appreciate edits to the questions: thank you. Why can the row-reduced echelon matrix $R$ only be identity matrix? I'm reading Linear Algebra by Hoffman, Kunze where the authors explained that a $n\times n$ matrix $A$ being invertible is equivalent to the fact that $A$ is row-equivalent to $n\times n$ matrix $R$ which is an identity matrix.  In the proof of the theorem, they wrote:     $$R= E_k\ldots E_2E_1 A$$ where $E_1,\ldots,E_k$ are elementary matrices. Each $E_j$ is invertible, and so $$A = E_1^{-1}\ldots E_k^{-1}~R\,. $$  ... Since, $R$ is a (square) row-reduced echelon matrix, $R$ is invertible if and only if $R=I\,.$  [...]   I couldn't get the conclusion, since any row of $R$ can't be zero, it has to be identity matrix $I\,.$ Why is it so?  Isn't there any other row-reduced echelon matrix other than the identity matrix having no zero row and invertible? Why is it so?