How do I setup a VPN server on Ubuntu 14.04 LTS with No-IP?
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Seeing as C# can't switch on a Type (which I gather wasn't added as a special case because is relationships mean that more than one distinct case might apply), is there a better way to simulate switching on type other than this?  void Foo(object o) {     if (o is A)     {         ((A)o).Hop();     }     else if (o is B)     {         ((B)o).Skip();     }     else     {         throw new ArgumentException("Unexpected type: " + o.GetType());     } } I would like to think that some of the software I'm writing today will be used in 30 years. But I am also aware that a lot of it is based upon the UNIX tradition of exposing time as the number of seconds since 1970.  #include &lt;stdio.h&gt; #include &lt;time.h&gt; #include &lt;limits.h&gt;  void print(time_t rt) {     struct tm * t = gmtime(&amp;rt);     puts(asctime(t)); }  int main() {     print(0);     print(time(0));     print(LONG_MAX);     print(LONG_MAX+1); }   Execution results in:   Thu Jan  1 00:00:00 1970 Sat Aug 30 18:37:08 2008 Tue Jan 19 03:14:07 2038 Fri Dec 13 20:45:52 1901           The functions ctime(), gmtime(), and localtime() all take as an argument a time value representing the time in seconds since the Epoch (00:00:00 UTC, January 1, 1970; see time(3) ).      I wonder if there is anything proactive to do in this area as a programmer, or are we to trust that all software systems (aka Operating Systems) will some how be magically upgraded in the future?  Update It would seem that indeed 64-bit systems are safe from this:  import java.util.*;  class TimeTest {     public static void main(String[] args) {         print(0);         print(System.currentTimeMillis());         print(Long.MAX_VALUE);         print(Long.MAX_VALUE + 1);     }      static void print(long l) {         System.out.println(new Date(l));     } }    Wed Dec 31 16:00:00 PST 1969 Sat Aug 30 12:02:40 PDT 2008 Sat Aug 16 23:12:55 PST 292278994 Sun Dec 02 08:47:04 PST 292269055   But what about the year 292278994? Is there a "smallest" divergent sum? Use the new helpcenter for the question/answer ban message Related:    The helpcenter has . It still links to the  for further details. Besides that, the question ban message .  Now that we have the helpcenter, could the following changes be implemented?   Link to the help center instead of the meta post Remove the link to the meta post from the help center, and instead incorporate its contents into the helpcenter itself Pretty-print a Map in Java HTML text input allow only numeric input I've been trying a simple recipe I found on the internet, which is a simple recipe consisting mostly of gelatin.  The problem is that the end result is basically just a fruit-flavoured jelly (Jell-O?), rather than the more chewy gummy-bears (Haribo) style of jelly confectionery.  Can anyone suggest what I need to do to make them less springy and more chewy.  It's all difficult to articulate!  Here's what I used for the first test-batch:   12 tbsp sugar 12/3 cup fruit juice 8 tbsp Golden Syrup 8 tbsp gelatin   soften the gelatin in 1/2 cup of cold water. place sugar, syrup and the juice in a pan and gently heat until sugar dissolves. Stir in the gelatin and stir until dissolved. Pour into moulds and wait until set.    Thanks mongodb group values by multiple fields This is a question from Stromberg related to Steinhaus' Theorem:     If $A$ is a set of positive Lebesgue measure, show that $A + A$ contains an interval.   I can't quite see how to modify the Steinhaus proof though. Finding a 2x2 Matrix raised to the power of 1000 Let $A= \pmatrix{1&amp;4\\ 3&amp;2}$. Find $A^{1000}$.  Does this problem have to do with eigenvalues or is there another formula that is specific to 2x2 matrices? Overnight charges for brokers holding stocks? I'm trying to learn about stock markets. I eventually want to invest a small amount over a long period. Yet, I notice on a lot of broker sites that they tend to charge an overnight fee for any stocks held over night. I presume this is every night thereafter?  I just wondered because it seems like a wall when you want to let your stock price grow, and an overnight charge eats into this. or, is this only the case for "CFD" stocks? I'm confused.  Any help?  Cheers In what segment (.BSS, .DATA, other) of an executable file are static variables stored so that they don't have name collision? For example:   foo.c:                         bar.c: static int foo = 1;            static int foo = 10; void fooTest() {               void barTest() {   static int bar = 2;            static int bar = 20;   foo++;                         foo++;   bar++;                         bar++;   printf("%d,%d", foo, bar);     printf("%d, %d", foo, bar); }                              }   If I compile both files and link it to a main that calls fooTest() and barTest repeatedly, the printf statements increment independently.  Makes sense since the foo and bar variables are local to the translation unit.  But where is the storage allocated?  To be clear, the assumption is that you have a toolchain that would output a file in ELF format.  Thus, I believe that there has to be some space reserved in the executable file for those static variables. For discussion purposes, lets assume we use the GCC toolchain. How can I recreate geometry using a photograph? How do you calculate this limit $\lim_{n\to\infty}\sum_{k=1}^{n} \frac{k}{n^2+k^2}$? How to find the value of $\lim_{n\to\infty}S(n)$, where $S(n)$ is given by $$S(n)=\displaystyle\sum_{k=1}^{n} \dfrac{k}{n^2+k^2}$$   is unable to calculate it.  This is a question from a questions booklet, and the options for the answer are--  $\begin{align} &amp;A) \dfrac{\pi}{2} \\ &amp;B) \log 2 \\ &amp;C) \dfrac{\pi}{4} \\ &amp;D) \dfrac{1}{2} \log 2 \end{align}$ In the time-dependent Schrodinger equation, $ H\Psi = i\hbar\frac{\partial}{\partial t}\Psi,$  the Hamiltonian operator is given by  $$\displaystyle H = -\frac{\hbar^2}{2m}\nabla^2+V.$$  Why can't we consider $\displaystyle i\hbar\frac{\partial}{\partial t}$ as an operator for the Hamiltonian as well? My answer (which I am not sure about) is the following:   $\displaystyle H\Psi = i\hbar\frac{\partial}{\partial t}\Psi$ is not an equation for defining $H$. This situation is similar to $\displaystyle F=ma$. Newton's second law is not an equation for defining $F$; $F$ must be provided independently.   Is my reasoning (and the analogy) correct, or is the answer deeper than that? When I open this ssh tunnel:  ssh -nXNT -p 22 localhost -L 0.0.0.0:8984:remote:8983   I get this error when trying to access the HTTP server running on localhost:8984:  channel 1: open failed: administratively prohibited: open failed   What does this error mean, and on which machine can you fix the problem? How to know if Mac OS X machine is being remotely viewed? Are getters and setters poor design? Contradictory advice seen I'm currently working on a simple game in Java with several different modes. I've extended a main Game class to put the main logic within the other classes. Despite this, the main game class is still pretty hefty.  After taking a quick look at my code the majority of it was Getters and Setters (60%) compared to the rest that is truly needed for the logic of the game.  A couple of Google searches have claimed that Getters and Setters are evil, whilst others have claimed that they are necessary for good OO practice and great programs.  So what should I do? Which should it be? Should I be changing my Getters and Setters for my private variables, or should I stick with them? CKEditor buttons not showing I'm using Drupal CKEditor module 7.x-1.13 and CKEditor 4.3.2. Everything is installed and appears to work fine... except that there are some buttons that don't appear despite being configured to do so, notably "Select All" and the justify left/right/centre/justified buttons. Here are the buttons as configured:    And here are the buttons as they appear: How to prove or disprove statements about sets Prove or disprove:  The set: $\{ \emptyset\}^{\Bbb N}$ has only one element.  The set $\emptyset^{\Bbb N}$ is empty.    I'm pretty sure both are true, for 1. all the natural numbers go to the empty set and that is the only element. Where as 2. all the natural numbers go to nothing so that's why it's empty. (Same as $ {\Bbb N}^{\emptyset} $ nothing goes to something is nothing (I think)). The problem is I have no idea how to show this so advice would be appreciated.  Edit: My defintion of a function is: $f:B\to A$ if  $(a_1,b),(a_2,b)\in f \ \Rightarrow \ a_1=a_2$ So for 2. I can simply say that: $(1,\emptyset),(2,\emptyset)\in f \Rightarrow a_1\neq a_2$  ?