Command to convert many images to one square image (not becoming a column or a row) Is this really duplicate? I have not yet found it anywhere.  For example:  I have 4 PNG images: image1.png, image2.png, image3.png, image4.png.  Every one of them is 200x200 pixels.  I want to convert them to image1234.png.  image1234.png is 400x400 pixels, what consist of:   image1.png is in the top-right. image2.png is in the top-left. image3.png is in the bottom-right. image4.png is in the bottom-left.
Merging two pictures Is there a tool in Ubuntu to automatically merge two images having a common strip? I need to scan a large image, which will not fit at once in the scanner. I was thinking about scanning it in two parts and hand-editing the result in Gimp to join them. But probably an automatic tool can do the same more quickly and better.  EDIT I think I may have not made my point clear. My difficulty is not aligning two images. My problem is that one has to compensate for the rotation or distortion introduced by the manual process of putting the sheet into the scanner, and an automatic tool should obtain more precise results at analyzing common patterns in the two images to rotate and align them seamlessly.
Evaluating $\lim_{n \to \infty} (1 + 1/n)^{n}$ I was recently thinking about how I could evaluate the famous limit of 'e' as I haven't ever seen a proof. I can't really find anything online so I've tried to evaluate the limit myself. And I was also thinking it would be nonsensical to use L'Hopital's rule, am I right?  So I did the following:  $$\lim_{n \to \infty} \left(1 + \frac{1}{n} \right)^{n} = \exp \left(\lim_{n \to \infty} n \cdot \ln \left(1 + \frac{1}{n} \right) \right)$$  $$=\lim_{n \to \infty} \exp \left( n \cdot \left( \frac{1}{n} - \frac{(1/n)^{2}}{2} + \cdots \right) \right)$$  $$= \lim_{n \to \infty} \exp \left( 1 - \frac{(1/n)}{2} + \cdots \right)$$  $$= e$$  I am not sure, is my logic correct or does it create circularity by taking logarithms and assuming $$f(x) = \exp \left( \ln f(x) \right)$$ ? How do I calculate the voltage needed to heat up a wire to a certain temperature? The wire I am using is standard temp. nitinol wire which needs to be heated up to 45 degrees Celsius in order to be effective (move). What voltage do I need to achieve this? I read about how to enable and disable services in Ubuntu and it seems that there are different possibilities to manage them.  The first method I found is update-rc.d to add new services to startup, which aims on the /etc/init.d folder and its contents.  The other one I found is to edit .conf files in the /etc/init folder.  What's the recommended way to enable / disable / add services and why?  Could you please give a short bulletproof step by step example on how to add a service in Ubuntu and enable and disable it? I can't seem to find a few of the Stones, so, is there a list available with the location of all the stones? Are shell scripts sensitive to encoding and line endings? What's the fixed size of the suggested edit queue? $\sqrt[31]{12} +\sqrt[12]{31}$ is irrational Prove that $\sqrt[31]{12} +\sqrt[12]{31}$ is irrational.   I would assume that $\sqrt[31]{12} +\sqrt[12]{31}$ is rational and try to find a contradiction.  However, I don't know where to start. Can someone give me a tip on how to approach this problem? What constitutes a legal block in volleyball in regard to it not counting as the first hit? Today in a match the setter set the ball too low for me to spike it, so I just dinked it over.  The bottom of the ball was lower than the top of the net at the point where I made contact.  When the defender made contact, again, the bottom of the ball was lower than the top of the net (the top of the ball was over the top of the net though).  I felt that this wasn't technically a block and that he shouldn't have been allowed to hit it a second time, but I wasn't sure so I just let it go.  Was this a legal block or should it have been our point when he hit it a second time in a row?  Edit:  I don't think I was clear about the part where, after I hit the ball, the ball travelled over the net onto the other team's side of the court.  The other player did not reach over the net so there is no issue there.  It's just an issue of whether or not their first contact was a block or a hit.  I believe it was not a block but I can't find a specific ruling to address it. What if I run a virus/trojan Windows EXE on Ubuntu with Wine? What color codes can I use in my PS1 prompt? I used several colors in my PS1 prompt such as   \033]01;31\] # pink \033]00m\]   # white \033]01;36\] # bold green \033]02;36\] # green \033]01;34\] # blue \033]01;33\] # bold yellow   Where can I find a list of the color codes I can use?  I looked at  but it didn't answer my question about a list of the actual codes.  It would be nice if there was a more readable form also.  See also The cardinality of $\{f\subseteq\mathbb R^2\mid f\colon\mathbb{R\to R}\text{ is a function}\}$ is strictly greater than the cardinality of $\mathbb R$ $SU(3)$ irreducible representations with tensor method Do citizens migrate closer to their workplace within the town? By using the Path tool (F2, 7) I have found some laborers walking very long to eat at home or to warm up in winter.  If I build a house close to a Quarry or a Mine, will Stonecutters or Miners move automatically to this house to avoid long walking distances between the workplace and home?  Or can I assign some citizens to houses closer to their workplace? Determine if the convergence of $f_n(x) = \sqrt{x^2 + \frac{1}{n^2}}$ is uniform. $f_n(x) = \sqrt{x^2 + \frac{1}{n^2}}$ converges pointwise in a set $E = [0, \infty)$ to $f(x) = x$.   This problem reminds me a lot of how $\frac{x}{n}$ fails to converge uniformly to $f=0$ on $[0,\infty]$, but does converge uniformly on $[0,a]$. However, when we proved that we used the definition of uniform convergence. I do not wish to do that here.  I wish to use the Weierstrass test here. And that is where I'm stuck. I cannot find $M_n = \sup\limits_{x \in E} |f_n(x)-f(x)|$. Can someone help me out here? jQuery autocomplete tagging plug-in like StackOverflow's input tags? What solutions accomplish the same auto-completion that SO uses for entering tags?  There are plugins that can handle one word but I haven't seen any that handle multiple words. I have a question about inheritance in Java.  I have two classes A and B , and class B, inherits from A:  public class A {      public A() {          System.out.println("Hi!");      } }   public class B extends A {      public B() {          System.out.println("Bye!");      }       public static void main(String[] args) {          B b = new B();      } }   When I run program B, the output is:  Hi! Bye!      Question : why the constructor of class A is invoked, when I create and object of class B ?    I know that B inherits everything from A - all instance or class variables, and all methods, and in this sense an object of B has all characteristics of A plus some other characteristics defined in B. However, I didn't know and didn't imagine that when I create an object of type B, the constructor of A is also invoked. So, writing this:  B b = new B();   creates Two objects - one of type B, and one of type A.  This is getting interesting,   can somebody explain why exactly this happens? How do I prevent the blank screensaver when using keyboard shortcut to lock the computer? EM with Binomial Attending graduate school at my undergraduate university I've been told by numerous people that (1) my undergraduate university will be disinclined to bring me on as a graduate student, and that (2) it's a bad idea to attend grad school where you completed your undergraduate degree, anyway.  Is that true? If so, why? Find the value of $\sum_{k=1}^{n}k\binom{n}{k}$ ?    I know that $\sum_{k=0}^{n}\binom{n}{k}= 2^{n}$ and so, $\sum_{k=1}^{n}\binom{n}{k}= 2^{n}-1$ but how to deal with $k$ ?