I want to cd into /var/named but it gives me a permission denied error, and when I want to use sudo to do this I am not permitted. What is the technical reason for this, and is it possible to do this some other way?
I tried to use sudo cd name_of_dir but am getting the error message:   sudo: cd: command not found   Is there any other way to enter a directory owned by another user which has 700 permission?
How to control the coordinates in Tikz & Matrix? I use Tikz with Matrix because I need to draw arrows and write on and beside the matrix. However, I don´t control the coordinates well other than using trail and error. For instance in the matrix below I have put an X at (0,0) and it is not in the centre of the matrix. However, if the matrix is 4x4 than it is in the centre. Is there any convenient way to know the coordinates? \documentclass[border=1cm]{standalone}  \usepackage{tikz} \usetikzlibrary{matrix}   \begin{document}  \begin{tikzpicture} \matrix(m) [matrix of math nodes, nodes in empty cells, nodes={minimum size=1cm, outer sep=0pt, text height=1.5ex, text depth=.25ex}] {  36     &amp;   &amp; 32    &amp;   &amp; 33    &amp;   \\         &amp;   &amp;       &amp;   &amp;       &amp;   \\  10     &amp;   &amp; 8     &amp;   &amp; 7     &amp;   \\         &amp;   &amp;       &amp;   &amp;       &amp;   \\  12     &amp;   &amp; 17    &amp;   &amp; 16    &amp;   \\         &amp;   &amp;       &amp;   &amp;       &amp;   \\  23     &amp;   &amp; 15    &amp;   &amp; 16    &amp;   \\     &amp;   &amp;   &amp;       &amp;   &amp;       &amp;   \\ };  \draw (m-1-1.north west) rectangle (m-8-6.south east);    % Lineas horizontales \foreach \i in {2,4,6,8} {   \draw (m-\i-1.south west) -- (m-\i-6.south east); }  % Lineas verticales \foreach \j in {2,4,6} {   \draw (m-1-\j.north east) -- (m-8-\j.south east); }  % dual ui \node [font=\color{red}] at (3.5,3) {$\ge 10$}; \node [font=\color{red}] at (3.5,1) {$\ge 8$}; \node [font=\color{red}] at (3.5,-1) {$=4$}; \node [font=\color{red}] at (3.5,-3) {$=3$};  % dual vj \node [font=\color{red}] at (-2.5,-5) {$\le12$}; \node [font=\color{red}] at (-0.5,-5) {$=12$}; \node [font=\color{red}] at (1.5,-5) {$=6$};  \node [font=\color{red}] at (0,0) {X};  \end{tikzpicture}     \end{document} The attribute image.itemtype has an invalid value I am using JSON-LD format for Structured data. In home page @type=website &amp; in details page @type=Article. Logo property of Organization section in details page showing following warning in Google Structured Data Testing Tool But home page is not although in both page value is same.      (The attribute logo.itemtype has an invalid value.)   Home page JSON-LD  &lt;script type="application/ld+json"&gt;     {     "@context": "http://schema.org",     "@type": "WebSite",     "url": "http://kothaboli.com/",     "name": ".....",     "alternateName" : "....",     "description" : "......",     "potentialAction": {         "@type": "SearchAction",         "target": "http://kothaboli.com/search?keywords={search_term_string}",         "query-input": "required name=search_term_string"     },     "sameAs":[         "https://www.facebook.com/kothaboliDotCom/",         "https://twitter.com/kotha_boli",         "https://plus.google.com/+kothaboli"     ],     "publisher" : {         "@type" : "Organization",         "name" : "....",         "alternateName": "...",         "logo": "http://kothaboli.com/media/1018/ka.jpg"         }     } &lt;/script&gt;     Details page JSON-LD      &lt;script type="application/ld+json"&gt;     {     "@context" : "http://schema.org",     "@type" : "Article",     "url": "http://kothaboli.com/interviews/intellectual/arundhati-roy/",     "name" : "... ....",     "headline":  "...--’",     "datePublished" : "7/26/2016 1:10:05 AM",     "dateModified" : "8/12/2016 1:50:54 AM",     "image" : "http://kothaboli.com/media/1088/33333333.jpg",     "articleSection" : "....",     "articleBody" : ".....’ ",     "mainEntityOfPage": "..",     "author" : {         "@type" : "Person",         "name" : "....",         "alternateName": "Arundhati Roy"         },     "publisher" : {         "@type" : "Organization",         "name" : "...",         "alternateName": "Kothaboli",         "logo": "http://kothaboli.com/media/1018/ka.jpg"         }     } &lt;/script&gt; What is the rule to convert the 'mm' notation to the 'optical zoom' notation? I searched a bit and found this one:  optical zoom = maximum focal length / minimum focal length   For example a 18-55mm lens would have a 3x optical zoom, and a 18-200mm lens would have a 11x optical zoom. Is that right? GeoServer cutting off symbols close to tile edges? How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work? Example of mailmerge package with an Excel spreadsheet I am looking for an example for using the  package to write a cover letter, with names and addresses on a spreadsheet. The package comes with an example, but you have to manually enter all the data. I was looking at the decomposition of Fibonacci numbers using the definition of $F_n = F_{n-1} + F_{n-2}$, and noted the pattern in the coefficients of the terms were Fibonacci numbers. It appears to hold, and I believe it's true, but I haven't seen a proof for it. Does one exist?  $F_n = 1F_{n-1} + 1F_{n-2}$ $F_n = 2F_{n-2} + 1F_{n-3}$ $F_n = 3F_{n-3} + 2F_{n-4}$ $F_n = 5F_{n-4} + 3F_{n-5}$ etc  This can be generalized to $F_n = F_xF_{n-(x-1)}+F_{x-1}F_{n-x}$ Floating Objects and Weight The Situation:  A ball is placed in a beaker filled with water and floats. It is also attached to the bottom of the beaker via a string.   The Question:  The ball is attached to the beaker, thus making the ball and beaker (and string included) a system. However, it is floating. Does the ball add to the weight of the beaker? In the Avengers movie, why is Hulk's behaviour inconsistent? In the Avengers movie, when      Bruce Banner is on the helicarrier, he becomes angry and transforms into the Hulk. Black Widow happens to be next to him and even though both are on same team, he attacks her and then Thor.  He becomes hostile to everyone on the ship.  But later on, in the fight against Chitauri troops, Hulk is very comfortably self-controlled.    Why is that?    The only thing I could think of is that it has been many days (a year?) since the Hulk had gotten angry, so he couldn't control himself.    But that's lame to be so puny when Bruce Banner was compared to Stephen Hawking in intelligence. What does "rigorous proof" mean? I have heard several times that some mathematician has given another and more rigorous for an established theorem, but I don't know what does it really mean and what differences makes it to be more 'rigorous'. My understanding of a proof is that a proof is some explanation to convincing others that a statement is true. If some proof is not rigorous, does it mean that while the proof is acceptable for many but it is not for everybody? If so, the proof is not correct since it going to be rejected by some people and it is not a proof at all. Or, does rigorous mean it uses more advanced tools? If so, why not any alternative (but simpler) proof is also acceptable as rigorous (which is more 'valuable' as well since it's simpler!)?   Saying those limited insight of mine, my questions are:   $1-$ What does rigorous proof mean, in general definition?  $2-$ In order to understand your answers, as an example I am re-writing three of the proofs for the compactness of the torus. Which of the following proofs are most rigorous, 'normal' and least rigorous; and why so?    Theorem: The torus $T^2$ is compact.  First proof: The torus is homeomorphic to the product space $S^1 \times S^1$. The circle $S^1$ is compact. Therefore the torus is the product of two compact spaces, and thus it is compact.   Second proof: The torus $T$ is the subspace of $\mathbb{R}^3$ obtained by rotating a circle about the $z$-axis. The torus is closed since given any point in its complement, there is an open ball of sufficiently small radius centered at that point and disjoint from the torus. Also, the torus is bounded since it is contained in the ball of radius $4$ centered at the origin. Since the torus is closed and bounded in $\mathbb{R}^3$, it is compact.   Third proof: The torus is homeomorphic to a space obtained as a quotient  space of the square by identifying opposite edges. The square is a closed and  bounded subset of $\mathbb{R}^3$ and therefore is compact. Furthermore, a quotient map on the square is a continuous function, and the image of a compact space under a continuous function is compact. Therefore the torus is compact.   Thanks a lot for your guidance. I need to process a large file, around 400K lines and 200 M. But sometimes I have to process from bottom up. How can I use iterator (yield return) here? Basically I don't like to load everything in memory. I know it is more efficient to use iterator in .NET. How can I compute the integral $\int_{0}^{\infty} \frac{dt}{1+t^4}$? I have to compute this integral $$\int_{0}^{\infty} \frac{dt}{1+t^4}$$ to solve a problem in a homework. I have tried in many ways, but I'm stuck. A search in the web reveals me that it can be do it by methods of complex analysis. But I have not taken this course yet. Thanks for any help. How to hide terminal output when executing a command? How can I install Ubuntu 13.04 + without USB, CD, DVD or Net? (hard drive only) I have an older i386 Sony Vaio desktop PC where the BIOS only allows boot from floppy, CD or very specific USB device types, none of which seem to recognize USB flash drives for some reason. Floppy is not an option because the drive no longer works and I have no media for it if it did. I've tried assorted CD and DVD drives, the CD drives all give read errors and DVD drives all say "unsupported emulation".  My next possible option that I would like to try, is to install the hard drive into another machine as a second HD and figure out a way to format it and save an Ubuntu installation to run from that HD once it is moved back into the target machine. IS this possible and if so, how would I go about doing so? The currently running machine uses Windows XP. I want to use $var in a shell brace expansion with a range, in bash. Simply putting {$var1..$var2} doesn't work, so I went "lateral"...   The following works, but it's a bit kludgey.    # remove the split files echo rm foo.{$ext0..$extN} rm-segments &gt; rm-segments source rm-segments   Is there a more "normal" way? In Russian roulette, is it best to go first? Assume that we are playing a game of Russian roulette (6 chambers) and that there is no shuffling after the shot is fired.  I was wondering if you have an advantage in going first?  If so, how big of an advantage?  I was just debating this with friends, and I wouldn't know what probability to use to prove it. I'm thinking binomial distribution or something like that.  If $n=2$, then there's no advantage. Just $50/50$ if the person survives or dies.   If $n=3$, then maybe the other guy has an advantage. The person who goes second should have an advantage.   Or maybe I'm wrong. I am writing a novel and fairly new to using LaTeX.  Please bare with me if this is a silly question.  I am working off of the novel demo LaTeX file using the TexWorks software.  I have inserted my words into the file.  When I run the LaTeX code, I get the error message saying "! LaTeX Error: File `novel.cls' not found."  Do I need to download this file from somewhere?  If so, where can I get it? Different results with Plot option "Evaluated" in V9 and V10 $ \int_1^2\int_1^2 \int_1^2 \int_1^2 \frac{x_1+x_2+x_3-x_4}{x_1+x_2+x_3+x_4}dx_1dx_2dx_3dx_4 $ Show that $E(X)=\int_{0}^{\infty}P(X\ge x)\,dx$ for non-negative random variable $X$ Show that for a non-negative random variable $X$,   $$\mathbb E(X)=\int_0^\infty \mathbb P(X\ge x) \, dx.$$   I started with  $$\mathbb E(X)=\int_0^\infty x \, dF(x)=\int_0^\infty \int_0^x dt\,dF(x).$$ This is my try.