I have been noticing some strange behaviour when I type characters like ' or the backtick. Whenever I type it, the &gt; symbol shows up everytime I type something, and everything I type seemingly does not do anything. But when I type the character again, it returns to normal.  user@debian:~$ ' &gt; command &gt; ' -bash: command : command not found user@debian:~$   What is this feature? As far as I know, the man page for bash did not say anything about this    Debian Jessie
Alright, when I run certain commands the wrong way, (misspelled, etc.) The terminal outputs this: &gt; instead of computername:workingfolder username$, and when I type enter it goes like this:  &gt;  &gt;  &gt;   That would be if I pressed enter 3 times.
How do I search for questions with specific tags?       For more information about searching, see &quot;&quot; in the . The parametric equation  $$\begin{align*} x(t) &amp;= \cos t\\ y(t) &amp;= \sin t \end{align*}$$  traces the unit circle centered at the origin ($x^2+y^2=1$).   Similarly,   $$\begin{align*} x(t) &amp;= \cosh t\\ y(t) &amp;= \sinh t \end{align*}$$  draws the right part of a regular hyperbola ($x^2-y^2=1$).  The hyperbolic trigonometric functions are very similar to the standard trigonometric function.  Do similar functions exist that trace parabolas (because it is another conic section) when set up as parametric equations like the above functions?  If so, are they also similar to the standard and hyperbolic trigonometric functions? So I have a program written in C++.  It can tell me how long it took to do all the calculations and it does a lot of quite heavy, multi-threaded calculation.   I've just noticed that if I run the program on the exact same machine, it takes around 20-21 seconds to do all the calculations if started from the TTY, and only about 0.2 seconds if I start it from GNOME terminal.  What is causing that? It's literally the exact same file on the same machine. a better way to express "an idea/thought suddenly came to me" What are some grandiloquent, or simply better, ways of expressing "an idea/thought suddenly came to me", or "an idea/thought struck me", or "I was struck by an idea/thought"? $x^2+y^2=z^n$: Find solutions without Pythagoras! I was presented with the following problem:      Prove that there exist solutions to $x^2+y^2=z^n$ for all $n$, with $x,y,z, n \in \mathbb{N}$   I showed that by taking any Pythagorean triple $x^2+y^2=z^2$ and multiplying by $z^{2(n-1)}$ we get $(z^{n-1}x)^2+(z^{n-1}y)^2=(z^2)^n$, which allows me to generate solutions easily for any value of $n$. I managed to find several similar questions on this site, such as  concerning the specific case $n=3$. I notice that all of these questions take a similar approach and start with a Pythagorean triple and use it to generate general solutions.  Is there a way to prove the statement (or better yet provide solutions to the equation) without first relying on Pythagoras? Can you take Gorrilla Glue in Hold Luggage on a plane? What are the differences between Generics in C# and Java... and Templates in C++? I mostly use Java and generics are relatively new. I keep reading that Java made the wrong decision or that .NET has better implementations etc. etc.  So, what are the main differences between C++, C#, Java in generics? Pros/cons of each? How do I create a villager with custom trade offers? How do I make a 2D game resolution independent? I'm working on a simple 2D game. I've finished the mobile phone version.  However, my boss wants the game to works on his RT. I'm doing the "conversion" but my buttons are in the wrong places, because I hard-coded the screen size, like this:   texture = game.Content.Load&lt;Texture2D&gt;("StartScreen");  mainFrame = new Rectangle(0, 0, game.GraphicsDevice.Viewport.Width, game.GraphicsDevice.Viewport.Height);   // button definitions  startbrect = new Rectangle(300, 258, 88, 88);  startbtext = game.Content.Load&lt;Texture2D&gt;("bplay");   In this example, mainframe is fine, but startbrect isn't, because I defined the size to match a Windows phone's screen. How can I handle responsive design when all Windows 8 phones' screens are different? Is there a formula or macro to calculate each time the good size? I have a question about the following passage on pg. 89 of Zee's QFT in a nutshell:     At first sight, what Dirac wanted does not make sense. The equation is supposed to have the form "some linear combination of $\partial_\mu$ acting on some field $\psi$ is equal to some constant times the field." Denote the linear combination by $c^\mu\partial_\mu$. If the $c^\mu$'s are four ordinary numbers, then the four-vector $c^\mu$ defines some direction and the equation cannot be Lorentz invariant.   The simplest equation I can construct that he is referring to is  $$(c^{\mu}\partial_{\mu}-m)\phi(x)=0, $$  for $m&gt;0$. Taking $\phi(x)\rightarrow\phi(\Lambda^{-1}x)$, and $c^{\mu}\rightarrow\Lambda^{\mu}_{\ \ \nu}c^{\nu}$. Then, the left term transforms like   \begin{align*} \Lambda^{\mu}_{\ \ \nu}c^{\nu}(\Lambda^{-1})^{\sigma}_{\ \ \mu}\partial_{\sigma}\phi(\Lambda^{-1}x) &amp;= \delta^{\sigma}_{\ \ \nu}c^{\nu}\partial_{\sigma}\phi(\Lambda^{-1}x)\\ &amp;=c^{\sigma}\partial_{\sigma}\phi(\Lambda^{-1}x). \end{align*}  Then, we have that   $$ (c^{\sigma}\partial_{\sigma}-m)\phi(\Lambda^{-1}x)=0.$$  But doesn't this show that the equation is Lorentz-invariant? What is true for a ring with exactly two right ideals Why does Newton's Third Law actually work? My father explained to me how rockets work and he told me that Newton's Third Law of motion worked here. I asked him why it works and he didn't answer. I have wasted over a week thinking about this problem and now I am giving up. Can anyone explain why Newton's Third Law works? For reference, Newton's third law:  To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. How do I access the index in a for loop like the following?  ints = [8, 23, 45, 12, 78] for i in ints:     print('item #{} = {}'.format(???, i))   I want to get this output:  item #1 = 8 item #2 = 23 item #3 = 45 item #4 = 12 item #5 = 78   When I loop through it using a for loop, how do I access the loop index, from 1 to 5 in this case? Increase resolution to 4K in VMware or Virtualbox I have a laptop with a 4K (3860×2160) display, but there are a lot of problems. A lot of virtualization programs aren't compatible with 4K resolution.  VMware Workstation and VirtualBox don't support 4K display in the list of the display's resolution. How I can set the resolution of the display in a virtual machine to 4K? How do you handle the varying sizes of filters in your kit? I have a variety of Nikon DX lenses that take differently sized filters. Most take 52mm filters, but there are a few that take larger 67mm or 77mm filters. The advice I've read most commonly online is to buy one filter size and get filter conversion rings to step up to that size filter. In my case, the largest size appears to be 77mm.  So, I walked into a couple local photo shops and asked about 52mm-77mm filter conversion rings and they looked at me like I had two heads. One guy suggested I stack a 52mm-67m and a 67mm-77mm. I have found 52mm-77mm rings online, so I know they exist.  Is this not a common thing to do? How does the stack exchange community handle the varying sizes of filters in their kit?  Thanks, PaulH Best way to migrate a huge SQL Server database with low downtime over network Problem definition  Our database server needs to be transferred to an other datacenter. It runs on Microsoft SQL Server 2012 Enterprise (64-bit) and contains two databases of about 2TB and 1TB.  Having little to no downtime for this would be ideal.  Workload  Those databases are used for a .NET website and are constantly getting updated.   Having it not available over the weekend would be acceptable though. The currently in use DB would remain the only one in use until the switch over to the new one.  That switch would ideally be made just by changing DNS entries to point to the new DB server while making sure the DB is not being updated.  Also, time taken by this operation does not really matter as long as the switch from one server to the other (downtime) is kept low.  Approaches considered   Backup and restore  This has been done in the past but involved a high downtime even though it was done through an internal network, so more efficiently than through Internet Log shipping  As far as I understand, this approach would minimize downtime by configuring a master/slave and transferring  an exact copy of the master DB to its slave being read only. As mentioned above, no access to the slave would be necessary and we just need a way to have a replica of the master DB without data corruption.   It also seems to be quite efficient in terms of resources utilization and wouldn't impact to much the master performance.   I might be wrong about this approach so feel free to correct me. Database mirroring  I'm not too aware of that approach but it seems like a valid option. No need to have real time sync and performance of the master is quite important so asynchronous would be the way to go if this approach were to be chosen. Other options?  That server runs directly on bare metal hardware so lower level solutions are unfortunately not an option. Maybe there is a better way to get this done?   Constraints  As described, those databases are quite big to the point they are hard to maintain but that's an other problem.  The versions of SQL Server will be the same (Microsoft SQL Server 2012 Enterprise 64-bit).  It will have to be transferred over network between two datacenters so most probably over Internet. Having disks sent from one site to the other for an initial sync is unfortunately not an option. Having some sort of security for the transfer would be ideal but we will do the best of this situation.  That should give a quite good overview of our needs for this task and hopefully some of you had to face that situation before. Ubuntu equivalent of system restore? Does it exist? Ubuntu n00b here.  I have created several disasters of the first order already.  I am getting ready to try to install opera - it is a very long and arduous process.  I am afraid - no - I am absolutely certain that I will damage something important.  How do I create a system restore point?  Does such a thing exist? Auxhook warning cannot patch document using AtBeginDocument instead I'm using subfiles within my report (written on sharelatex), when I compile a subfile it produces a warning. Am I doing something wrong or is this normal?  Example  \documentclass[report.tex]{subfiles} % \usepackage{acronym} \begin{document}  some text  \end{document}   Error     /usr/local/texlive/2015/texmf-dist/tex/latex/oberdiek/auxhook.sty   Package auxhook Warning: Cannot patch \document, using \AtBeginDocument instead.   When I compile the main document it does not produce this warning.  The raw log file produces this warning     ......   Package: auxhook 2011/03/04 v1.3 Hooks for auxiliary files (HO)   Package auxhook Warning: Cannot patch \document,   (auxhook)                using \AtBeginDocument instead.   ) (/usr/local/texlive/2015/texmf-dist/tex/latex/oberdiek/kvoptions.sty   Package: kvoptions 2011/06/30 v3.11 Key value format for package options (HO)   ....    Packages  I'm using the following packages:    \documentclass[whitelogo]{tudelft-report}   % Used for referencing   \usepackage{natbib}   % For writing remarks in the text (is this going to be used?)   \usepackage{changes}   % used to write and render different subfiles   \usepackage{subfiles}   % used to draw boxed problems   \usepackage{mdframed}   % for subcaptions in combined figures   \usepackage{subcaption}    % used for Epigraphs of course   \usepackage{epigraph}   % Makes weblinks clickable   \usepackage{hyperref}   % used to display pictures   \usepackage{graphicx}   % used to add urls with strange symbols   \usepackage{grffile}   % used for H command in figures   \usepackage{float}   % used for tickz pictures (Causes a warning)   %\usepackage{pgfplots}   %used for the acronym page [printonlyused,withpage] are options   \usepackage{acronym}    % ######################### open section for code appendix #######################   \usepackage[utf8]{inputenc}   \usepackage{listings}   \usepackage{color}   \definecolor{codegreen}{rgb}{0,0.6,0}   \definecolor{codegray}{rgb}{0.5,0.5,0.5}   \definecolor{codepurple}{rgb}{0.58,0,0.82}   \definecolor{backcolour}{rgb}{0.95,0.95,0.92} Let $f$ be a continuous function on $[0,1]$ such that $f([0,1])=[0,1]\times[0,1].$ Then show that $f$ is not one-one.  Hints will be appreciated. I've been try to download Xcode for work, but for some reason the Mac App Store is giving me a bit of trouble. Activity monitor shows some network usage, but in Launchpad it seems the download isn't moving.   When I go to the purchases panel of the Mac App Store, I see this.     No status, no pause button, in fact - the button has no text on it! I've tried restarting the App Store, restarting my computer, even removing the com.apple.appstore folder in /var/folders but alas, no luck.  Can anyone diagnose the issue? When I removed com.apple.appstore, Xcode still showed up on Launchpad, and clicking on it did nothing - it was frozen in time. So can I kill off this partial download and start new?