How to check if element exists with SimpleXML?
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Do superheroes/villains like Quicksilver or Flash with super speed get tired due to running? How do I install the ubuntu-restricted-extras package? AWS S3, Paperclip missing required :bucket option Relationship between SVD and PCA. How to use SVD to perform PCA? Principal component analysis (PCA) is usually explained via an eigen-decomposition of the covariance matrix. However, it can also be performed via singular value decomposition (SVD) of the data matrix $\mathbf X$. How does it work? What is the connection between these two approaches? What is the relationship between SVD and PCA?  Or in other words, how to use SVD of the data matrix to perform dimensionality reduction? What's the meaning of this present perfect sentence? How to install the most common plugins? I have a chain object. And i have a curve it follows. I got it to work for following curve, but chain object is not circles but both parts are more like stretched circles (ovals). Object i made with 2 toruses one rotated 90 degrees and then joined them together. I tried single torus too. But same issue. on a curve it just looks stretched oval. What can be the issue?   Thanks I am trying to draw the below given figure. Please help me to plot it in Tikz. I am only able to plot concentric circles. . I would like to have different colors in between different circles. Also, the text should be along the curve. The arrow in between the two concentric circles does not have to overlap with the circle on the right hand side.  I would be grateful if you could help me in plotting this in Tikz. Please let me know if you need more information. Thanks!  \documentclass[conference]{IEEEtran}  \ifCLASSINFOpdf  \else  \fi  \usepackage[usenames,dvipsnames]{color} \usepackage[T1]{fontenc} \usepackage{tikz} \usetikzlibrary{positioning} \usetikzlibrary{arrows} \usetikzlibrary{shapes.multipart} \usepackage[caption=false]{subfig} \usepackage{tabularx,tikz} \usepackage{graphicx} \usepackage{color} \usepackage{pdfpages} \begin{document}  \title{Practice Tex}   \maketitle  \section{Introduction}  \begin{figure} \begin{center} \begin{tikzpicture}     \draw(0,0) circle (0.4cm)   node[draw=none,sloped,above]{cxvzxcv};         \draw(0,0) circle (0.75cm) node[draw=none,sloped,above]{ratio};    \draw(0,0) circle (1.25cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,2.2) {22};    \draw(0,0) circle (2cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,3.8) {33333};    \draw(0,-9) circle (0.4cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-9) {fsgsdgf};      \draw(0,-9) circle (0.75cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-7.8) {fgdsfg};    \draw(0,-9) circle (1.25cm) node[midway,sloped] at (0,-9) {dfsdfad};    \draw(0,-9) circle (2.8cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-6.4) {dfsdfsd};    \draw(0,-9) circle (3.2cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-6) {dfsdfsd};    \draw(0,-9) circle (3.6cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-5.6) {sfdsfd};    \draw(0,-9) circle (4.4cm);   \node[draw=none,align=center, font=\scriptsize,text width = 1.25cm] at (0,-4.8) {sdfsf};     \pgfsetlinewidth{3pt}    \draw [-implies][-&gt;] (0,-4) -- (0,-4.6);   \end{tikzpicture}  \end{center} \end{figure} \end{document} When for the first time A new question I answer This haiku appears:     Little slab of meat   In a wash of clear jelly   Now I heat the pan   Such a message is Very strange; is anyone Seeing the same thing?  Have not seen again. Came and went like the wind does! Why I am so blessed? What happened to Rhaegal? In Game of Thrones S08E03 ("The Long Night"), the Night King's dragon tore at the one Jon Snow rides (Rhaegal). He falls off of it and we don't see the dragon anymore, is it dead? Is it possible in Latex to make a triangular hat? The one that is used in math over three letters representing points to indicate a triangle.  Something like: SQL comma-separated row with Group By clause Why do I get (author?) when I use \citet with natbib? I would like to show the author names using \citet but I get just the reference number. Here is a minimal code:  \documentclass{report} \usepackage[utf8]{inputenc} \usepackage[english]{babel} \usepackage{natbib}  \begin{document}   The author \citet{toschi09} has shown that ..  \bibliographystyle{plain} \bibliography{foo}  \end{document}   And here is foo.bib  @article{toschi09, author = {Toschi, F. and Bodenschatz, E.}, title = {Lagrangian Properties of Particles in Turbulence}, journal = {Annual Review of Fluid Mechanics}, volume = {41}, number = {1}, pages = {375-404}, year = {2009},  }   What I get is:     The author (author?) [1] has shown that ..   Any help will be more than welcome, thank you! How to resolve BackgroundContainer.dll error on startup? When I start my desktop it gives me an error about BackgroundContainer.dll.    How to get rid of it?  I found nothing when i started regedit.exe and searched (F3 or CTRL+F) for BackgroundContainer.dll Correct location for piping and redirecting output in find -exec? I'm using find with the -exec option in console, on FreeBSD (for example, find . -exec sha1 {} \;).   How do I correctly place (and if needed, escape) redirect and other execution control symbols that could syntactically apply to either of the exec command or the find command, such as > >> | and &amp;, where I might want the symbol to apply to the find or the exec commands on different occasions?  On the same theme, what is the syntax if I want to use tee to view the output of the -exec commands on the console (to watch progress) and also appended to a file (for later use)?   (I know shells vary but hopefully the most used shells such as sh/csh are quite similar?)  Update:  In part, I want to learn if nested find -exec can be done without scripting, as a simple command. Here is the use-case that prompted the questio :   outer find: find all subdirs matching DIR_MATCH_TEXT in DIR1  inner find: for each matching subdir found in the outer loop (call it DIR2), execute the commandfind DIR2 -name "FILE_MATCH_TEXT" -exec sha1 {} \; &gt;&gt; DIR1/DIR2_hashes.txt   The aim being to create a set of files, one for each matching subdir, containing the output of some find -exec action on that subdir.  By this I mean that, if /backups contains /jan2017 and /feb2017, the result will be two files at /backups/jan2017_hashes.txt and /backups/feb2017_hashes.txt, with jan2017_hashes.txt containing the output from sha1 for (say) all .pdf files in /backups/jan2017, and feb2017_hashes.txt containing the output from sha1 for all .pdf files in /backups/feb2017.  From replies so far I gather the outer find would have to use a shell call as the argument to -exec? How can I install an app given only its APK file? I downloaded the APK file for an app to my PC.  How can I install it on my phone? Prove that the function : $f(x) = x$ when $x$ is rational and $f(x) = 1 - x$ when $x$ is irrational is continuous at $x = \frac{1}{2}$  To prove the continuity it is necessary to prove that for every $\epsilon$ there exists a $\delta$ such that $|f(x) - f(\frac{1}{2})| &lt; \epsilon$ whenever $|x -c| &lt; \delta$ $- (1)$ Now if we choose $a  € (\frac{1}{2} - \delta, \frac{1}{2} + \delta)$ and also $a $ is rational and choose $\epsilon &lt; |a - \frac{1}{2}|$ then condition in $(1)$ is not satisfied. How to move from here? Do null and alternative hypotheses have to be exhaustive or not? I saw a lot of times claims that they have to be exhaustive (the examples in such books were always set in such way, that they were indeed), on the other hand I also saw a lot of times books stating they should be exclusive (for example $\mathrm{H}_{0}$ as $\mu_1=\mu_2$ and $\mathrm{H}_{1}$ as $\mu_1&gt;\mu_2$) without clarifying the exhaustive issue. Only before typing in this question I found somewhat stronger statement on the  -- "The alternative need not be the logical negation of the null hypothesis".  Could someone more experienced explain which is true, and I would be grateful for shedding some light on the (historical?) reasons for such difference (the books were written by statisticians after all, i.e. scientists, not philosophers). Show address bar w. full path in Nautilus instead of breadcrumbs bar Am I able to use a controller to play the PC version of Minecraft? If so, can I just plug it in and play or do I have to do something else before being able use one?