Is there anything such as LaTeX documentation? When I am looking for some syntax on google, I only get to forums, but never a site with actual documentation, such as when looking for the meaning of \thechapter or \let. It seems everyone knows meaning of things like secnumdepth but where does this knowledge come from other than going through the sources and hoping the developer left a useful comment? I know for packages to go to ctan but other than that...
Which book (free or otherwise) was the most useful to you when you started learning LaTeX?  I am frequently asked this question by friends who want to learn LaTeX, and I recommend the book which got me started, , but I feel that there might be better options around.  Also see .
I created the following matrix with , and I would like to add at the bottom (respectively right) something like an underbrace (resp. "rightbrace") under each of the two blocks, together with a number specifying the number of columns (resp. rows) of the block. This amounts to two braces on the bottom and two on the right, and each brace should have a number below (resp. at the right) of it.  I did not find anything about that on the easybmat manual. I think I see how to do the braces with the  package, but then I am not able to create the block structure of the matrix in the first place.  \documentclass{article} \usepackage{easybmat} \begin{document} \[  M(z)= \left[ \begin{BMAT}[5pt]{c|c}{c} \begin{BMAT}[5pt]{c:c:c}{ccccccc} &amp; &amp; \\ &amp; &amp; \\ &amp; &amp; \\ v_1 &amp; \dots &amp; v_m \\ &amp; &amp; \\ &amp; &amp; \\ &amp; &amp; \end{BMAT} &amp; \begin{BMAT}{c}{c|c} \begin{BMAT}[5pt]{c:c:c}{ccc} &amp; &amp; \\ w_1(a) &amp; \dots &amp; w_n(a) \\ &amp; &amp; \end{BMAT} \\ \begin{BMAT}[10pt]{c}{c} B(z) \end{BMAT} \end{BMAT} \end{BMAT}  \right] \] \end{document}     This is more or less what i wish: Why does the order of summation of the terms of an infinite series influence its value? I was looking through my lecture notes and got puzzled by the following fact: if we want to find the value of some infinite series we are allowed to rearrange only the finite number of its terms. To visualize this consider the alternating harmonic series: $$\sum_{n=1}^\infty(-1)^{k-1}\frac1k=1-\frac12+\frac13-\frac14+\frac15-+\dots=0.693147...$$  But if we rearrange the terms as follows the value of the series gets influenced by this action: $$1+\frac13-\frac12+\frac15+\frac17-\frac14+\dots=1.03972...$$  So commutativity of addition isn't true on infinity? How was it obtained and how can it be proved? Every time I try update (using sudo apt-get update) my Ubuntu I get this problem:  W: The repository 'cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1) xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. W: The repository 'ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-i386/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.   How can I fix it? I use Ubuntu 16.04 LTS After T-2, why not send back another T-800? Trying to find a Sci-Fi movie, probably from the 50's or 60's I’m trying to identify a movie I saw when I was very young.  It was a “Saturday Matinee” playing on one of the local stations, and I likely watched it in the late 60’s.  So I expect that the movie is from the 50’s or 60’s.  I watched it in black and white, but it could have been a color movie on a black and white set. I clearly recall a scene where scientists enter a lab and some see something move past them in a blur.  Later in the movie, they come upon themselves in the same lab where they appear to be frozen and not moving.  Then they notice that their “other selves” are moving, just almost inperceptibly slowly.  They are encountering themselves but at a completely different time scale. Unfortunately, I don’t recall much else about the movie, just the idea that they encounter themselves once with the others flashing past, and again seemingly not moving at all.  If this rings any bells with anyone, I’d love some pointers to try to track this movie down. At what age does a toddler stop being a toddler? Compiling PHP 5.1.6 with PDO MySQL Prove that the subsequence of a convergent series with nonnegative terms converges When thinking about travelling, I often have to think about a place to visit, and then look up visa rules for that particular country. This can be a fairly painful process because official government sites can often be hard to find, and advice on (say) guidebooks or Wikitravel tends to be generic.  Is there any resource where I can enter my nationality/residency, and then look up a list of visa rules for various countries? How to install the latest Arduino IDE? I have an Arduino UNO, which I need to get working with Ubuntu.  Can somebody explain to me the steps required to install the IDE on Ubuntu? I need to get a history of which processes have run on my Windows machine, and when they were run.  However, I cannot use any third-party software, as I cannot guarantee that it will always be running.  Is there any way to get this information only using Windows built-in functionality? Cycles not rendering image or movie clip used as background in the viewport Find $\lim\limits_{x \to \infty} \frac{x}{(\log{x})^n}$ Find $\displaystyle \lim_{x \to \infty} \dfrac{x}{(\log{x})^n}$.   My book says that $\displaystyle \lim_{x \to \infty} \dfrac{(\log{x})^n}{x} = \lim_{y \to \infty} \dfrac{y^n}{e^y} = 0$, but I don't see how that is true. I want to assign a class attribute via a string object - but how?  Example:  class test(object):   pass  a = test() test.value = 5 a.value # -&gt; 5 test.__dict__['value'] # -&gt; 5  # BUT: attr_name = 'next_value'  test.__dict__[attr_name] = 10 # -&gt; 'dictproxy' object does not support item assignment Check if table exists in SQL Server I want a true deep copy. In Java, this was easy, but how do you do it in C#? Story about a future with races Alternative Method to Acquire El Capitan Upgrade Should multiverse theories be rebranded as meta physics? I answered a question here with a quote with the following quote from Cosmologist George Ellis.     “Similar claims [about a multiverse] have been made since antiquity by many cultures. What is new is the assertion that the   multiverse is a scientific theory, with all that implies about being   mathematically rigorous and experimentally testable. I am skeptical   about this claim. I do not believe the existence of those other   universes has been proved—or ever could be. Proponents of the   multiverse, as well as greatly enlarging our conception of physical   reality, are implicitly redefining what is meant by ‘science.’”—pg 39      “For a cosmologist, the basic problem with all multiverse proposals is the presence of a cosmic visual horizon. The horizon is   the limit to how far away we can see, because signals traveling toward   us at the speed of light (which is finite) have not had time since the   beginning of the universe to reach us from farther out. All the   parallel universes lie outside our horizon and remain beyond our   capacity to see, now or ever, no matter how technology evolves. In   fact, they are to far away to have had any influence on our universe   whatsoever. That is why none of the claims made by multiverse   enthusiasts can be directly substantiated.”—pg 40-41      “A remarkable fact about our universe is that physical constants have just the right values needed to allow for complex structures,   including living things. Steven Weinberg, Martin Rees, Leonard   Susskind and others contend that an exotic multiverse provides a tidy   explanation for this apparent coincidence: if all possible values   occur in a large enough collection of universes, then viable ones for   life will surely be found somewhere. This reasoning has been applied,   in particular, to explanation the density of the dark energy that is   speeding up the expansion of the universe today. I agree that the   multiverse is a possible valid explanation for the value of this   density; arguably, it is the only scientifically based option we have   right now. But we have no hope of testing it observationally.”—pg 42      “All in all, the case for the multiverse is inconclusive. The basic reason is the extreme flexibility of the proposal: it is more a   concept than well-defined theory. Most proposals involve a patchwork   of different ideas rather than a coherent whole. The basic mechanism   for eternal inflation does not itself cause physics to be different in   each domain in a multiverse; for that, it needs to be coupled to   another speculative theory. Although they can be fitted together,   there is nothing inevitable about it. … Nothing is wrong with   scientifically based philosophical speculation, which is what   multiverse proposals are. But we should name it for what it is.”—pg 43   Now with this in mind if these theories cannot be independently verified should their truth not lie in  method outside physics or what is also known as meta physics? How to repair Ubuntu installation after interrupted dist-upgrade without losing any custom settings?