Inertia of a quadratic form
Proving that two matrices are congruent, in order to establish a rank and signature result.
Please add TeX rendering on the Android app Erf as term for plot of land in a town or city. Is this word only used in southern Africa? How do I clear keyboard/autocorrect history on the Galaxy s4? I let my younger cousins play on my S4 from time to time, but now I have found that all the words they have used are the first to come up when I use my phone to text. It has gotten quite irritating. Samsung seems to have very hard to find settings compared to my old Sony Ericsson so I cannot find where to get rid of the word history typed onto my phone's keyboard. "Authoring" versus "Writing" In my area of work the word author as a verb has become quite common. However, it seems to have a subtly different meaning than plain vanilla write. For example, one does not write software unit tests; one authors them.  Can anyone offer a clear distinction between the two words? Has author as a verb become a common usage outside of the field of computer software? How is Mono magical? I'm learning C#, so I made a little C# program that says Hello, World!, then compiled it with mono-csc and ran it with mono:  $ mono-csc Hello.cs $ mono Hello.exe Hello, World!   I noticed that when I hit TAB in bash, Hello.exe was marked executable. Indeed, it runs by just a shell loading the filename!   Hello.exe is not an ELF file with a funny file extension:  $ readelf -a Hello.exe readelf: Error: Not an ELF file - it has the wrong magic bytes at the start $ xxd Hello.exe | head -n1 00000000: 4d5a 9000 0300 0000 0400 0000 ffff 0000  MZ..............   MZ means it's a Microsoft Windows statically linked executable. Drop it onto a Windows box, and it will (should) run.  I have wine installed, but wine, being a compatibility layer for Windows apps, takes about 5x as long to run Hello.exe as mono and executing it directly do, so it's not wine that runs it.  I'm assuming there's some mono kernel module installed with mono that intercepts the exec syscall/s, or catches binaries that begin with 4D 5A, but lsmod | grep mono and friends return an error.   What's going on here, and how does the kernel know that this executable is special?    Just for proof it's not my shell working magic, I used  (aka sh) to run it and it still runs natively.    Here's the program in full, since a commenter was curious:  using System;  class Hello {   /// &lt;summary&gt;   ///   The main entry point for the application   /// &lt;/summary&gt;   [STAThread]   public static void Main(string[] args) {     System.Console.Write("Hello, World!\n");   } } 80's Animated movie: An old man joins mission to save a boy stranded on a hostile world A guy on a space ship picks up a distress call, a boy is stranded on a planet with a hostile environment. He &amp; his crew go to the rescue, stopping on the way to pick up an old man who comes with them. Most of the top of the old guy's skull is metal, from an old injury.  They've various adventures on the way (their ship is boarded by pirates/bandits/hostile forces at one point).  They get to the planet with the boy. They've limited time to save him as the planet is being moved back in time. (I can't remember why) When they find the boy, he's being attacked by giant wasp-type-things.   The boy is injured on the top of his head. The old guy dies protecting him. The boy gets shifted back in time with the planet and - you guessed it - survives, grows up and turns out to be the old guy.  Now that I've remembered some of it, the bits I can't remember are driving me crazy. I'd love to see this again, if I could identify it I might be able to track down a copy.  I'd swear I saw this mid 80's on morning TV, but it I could be out by 5 years either way. Thanks What do I need in a camera to take non-blurry photos of a fast-moving child? I'm a mom who is obsessed with taking photos of my now 2 year old daughter.  I currently have a Nikon j1 which I like, but I find the shutter speed is still a bit slow and when you're trying to take photos of a speedy little girl, I end up with a lot of blurry images.  So I'm looking for a camera with a very fast shutter speed that will allow me to take good photos of a very fast moving child.  Also that can take photos in low light. I've been looking at the canon eos rebel but I'm not sure. Would like it to be able to take videos as well. Any advice? Trigger to check for duplicate contacts on lead conversion I'd like to write a Lead trigger, to check for duplicate Contacts before inserting the lead, or converting it.   Contacts fields I'd like to check:   Firstname - should not be the same as the leads name Lastname - should not be the same as the leads name Email - should not be the same as the leads phone   After checking these fields &amp; failing to find a duplicate, only then should the lead be converted. Given the length ot the sides $a , b$ and $c$  of $ \triangle ABC$.  What is the length of the radius of the circumcribed circle?  After some formula substitution I came to the monster formula:  $$ \frac {a b c}{\sqrt{2a^2b^2+2a^2c^2+2b^2c^2-a^4-b^4-c^4}} $$  Can this formula be simplified? I'm adding a title clock in the foot line of a beamer slide, if I compile it with pdfLaTeX it works fine; while the clock doesn't align in the middle vertically if compiling with XeLaTeX. How can I fix this.  Here is my MWE:  \documentclass[10pt]{beamer} \usepackage[font=Times,timeinterval=1]{tdclock} \usetheme{Madrid} \title{Title} \author{Authors} \institute{Institute} \date[\initclock\tddate\ \ \tdtime]{\today} \begin{document} \frame{\titlepage} \end{document} Different ways to execute a shell script There are several ways to execute a script. The ones I know are: /path/to/script # using the path (absolute or relative) . script        # using the . (dot) source script   # using the `source` command  Are there any other way? What are the differences between them? Are there situations that I must use one and not another? Do these leaves signify anything? Closed ball not a manifold. My book on differential geometry claims that a closed ball in $\Bbb R^n$ can never be a differentiable manifold because of the boundary points. The book doesn't really give an explanation for why this is true. Could someone provide more details please? thanks Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).  We're building a web API that's programmatically generated from a C# class. The class has method GetFooBar(int a, int b) and the API has a method GetFooBar taking query params like &amp;a=foo &amp;b=bar.   The classes needs to support optional parameters, which isn't supported in C# the language. What's the best approach? How do I calculate someone's age based on a DateTime type birthday? Given a DateTime representing a person's birthday, how do I calculate their age in years? My Ubuntu 14.04 is stuck when trying to login my desktop. The screen goes black and soon after that the login screen comes back.   I followed all steps in  but the issue was not solved. What is the name for the grammatical device of putting "not" after a verb to negate it? Which application does the vi command open? When you type vi in the terminal, the following output is shown  ~                             VIM - Vi IMproved                                 ~                                                                              ~                               version 7.3.547                                  ~                           by Bram Moolenaar et al.                             ~           Modified by pkg-vim-maintainers@lists.alioth.debian.org              ~                 Vim is open source and freely distributable                    ~                                                                                ~                        Help poor children in Uganda!                                                                                So according to this, vi must be launching VIm. But when you type  vim it gives  aditya@aditya-desktop:~$ vim The program 'vim' can be found in the following packages:  * vim  * vim-gnome  * vim-tiny  * vim-athena  * vim-gtk  * vim-nox Try: sudo apt-get install &lt;selected package&gt;   This shows that vim is not installed. Notably man vi and man vim launch the same man pages.  So what does the vi command actually launch? Removing spaces between "words" in math mode Check if specific id element exist