C/C++: How to print a stack trace?
How to automatically generate a stacktrace when my program crashes
Use mathematical induction to prove that 6(n+2) + 7(2n+1) is divisible by 43 for n >= 1.  So start with n = 1:  6(1+2) + 7(2(1)+1) = 63 + 73 = 559 -> 559/43 = 13. So n=1 is divisible  Let P(k): 6(k+2)+7(2k+1) , where k>=1  Show that P(k+1): 6((k+1)+2) + 7(2(k+1)+1) is true  = 6(k+1+2) + 7(2k+2+1)  = 6(k+3) + 7(2k+3)  I'm unsure where to go from here, I've tried several directions after this but have got nowhere. I don't know how to get the 43 or 559 out the front.  Any help would be great postfix doesn't work after iptables set up Trying to run , embedded Tomcat instance fails.  Error seems to appear here:    Apr 17, 2015 2:13:47 AM org.apache.catalina.startup.HostConfig deployDescriptor  INFO: Deploying configuration descriptor /opt/OpenForisCalc/calc-server/tomcat/conf/Catalina/localhost/calc.xml  Apr 17, 2015 2:13:58 AM org.apache.catalina.core.StandardContext startInternal   SEVERE: Error listenerStart   Then if messes up with the rest (this repeats a lot):  Apr 17, 2015 2:13:58 AM org.apache.catalina.core.StandardContext startInternal  SEVERE: Context [/calc] startup failed due to previous errors Appropriate data transformation How to compute $\lim\limits_{n\rightarrow \infty} \{(2+\sqrt{3})^{n}\}$, where $\{x\}$ is the fractional part of $x$? I've stumbled upon the following problem:  $$\lim_{n\rightarrow \infty} \{(2+\sqrt{3})^{n}\}$$  where "{}" notates the fractional part.  I've never studied this kind of problem, there exists any reference that I could read about this type of problem? Finding net magnetic and electric force on charged particle This is from my textbook, it is not an assigned problem, but I want to understand.   It says:      Consider the situation in the figure, in which there is a uniform electric field in the x direction and a uniform magnetic field in the y direction. For each example of a proton at rest or moving in the x, y, or z direction, what is the direction of the net electric and magnetic force on the proton at this instant?   I believe I need to use the equation   $$ F_{net}=(q\overrightarrow{E})+q(\overrightarrow{v} \times \overrightarrow{B}) $$  But I'm not sure exactly how. We've just started to learn about this, and I want to get a head start. Could anyone put me on the right track? What is the lowest level of mathematics required in order to understand how encryption algorithms work? Prove that if $a$ and $b$ are odd, coprime numbers, then $\gcd(2^a +1, 2^b +1) = 3$ Prove that if $a$ and $b$ are odd, coprime numbers, then $\gcd(2^a +1, 2^b +1) = 3$.   I was thinking among the lines of:  Since $a$ and $b$ are coprime numbers, $\gcd(a,b)=1$. Then there exist integers $x$ and $y$ such that, $ax+by=1$.   Then, $a=(1-by)/x$, $b=(1-ax)/y$  So if I write $2^a+1$ as:  $2^{(1-by)/x}+1$  Then can I say that the above expression is equivalent to 0 (mod 3)? How to get apache to send a 404 based on no matching VirtualHost section (based on ServerName) being found? I am rebuilding an old server.  Only one of the five old sites need to go live and all five of the old sites point to the same IP address.  Unfortunately any time a request is made for one of the old sites via their own unique domain names they are passed the pages from the one site that I'm trying to make live.  I would just like the old sites to display a 404 instead of the one site that I'm actually trying to make live.  As an example:   Site 1 (192.168.0.1) [www.first.com] Site 2 (192.168.0.1) [www.second.com] Site 3 (192.168.0.1) [www.third.com]   I want to move site 1 live again.  So I turned on apache on the machine with the IP address of 192.168.0.1, with all of site 1's files in the /var/www directory.  When I browse to 192.168.0.1 or www.first.com I correctly see site 1. When I browse to www.second.com and www.third.com I also receive site 1 which is the problem.  Is there a way I can 404 any request which comes in without www.first.com?  Here is my sites-available:  NameVirtualHost *:80  LogFormat "%h %l %u %t \"%r\" %&gt;s %b" common  &lt;Files ~ "^\.ht"&gt;     Order allow,deny     Deny from all     Satisfy All &lt;/Files&gt;  &lt;Directory /&gt;   Order Deny,Allow   Deny from all   Options None   AllowOverride None   Options None &lt;/Directory&gt;  &lt;Directory /var/www&gt;   Order Allow,Deny   Allow from all &lt;/Directory&gt;  &lt;VirtualHost *:80&gt;         ServerName first.com         ServerAlias www.first.com         DocumentRoot /var/www         ErrorLog /var/log/first.com.err         CustomLog /var/log/first.com.log common &lt;/VirtualHost&gt;  &lt;VirtualHost _default_:*&gt;         ServerName unknown         DocumentRoot /var/www_404 &lt;/VirtualHost&gt; As expected, Nvidia drivers have reduced my customizations. I can't login to Unity 3D session. I can't find any content to help me to uninstall the driver and I don't know what to do as I have never uninstalled them before. Can I declare a duplicate page via javascript for google? Most sources of documentation state that one can declare a webpage a duplicate of another by applying this tag on the duplicate page:  &lt;link rel="canonical" href="(absolute URL to original page)"&gt;   I could generate the above tag via the script below:  &lt;script&gt; var l=document.createElement('Link'); l.rel='canonical';l.href='(absolute URL to original page)'; document.getElementsByTagName('head')[0].appendChild(l); &lt;/script&gt;   My question is, would google be able to process this javascript and believe I'm declaring the page as a duplicate page? or would I be forced to use the link tag in the header?  I ask because I'm trying to reduce the unnecessary bytes required to be processed before the actual user readable content begins. How can I delete a symbolic link? I created a symlink using mklink.  Now I need to change it but I can't figure out how to delete it so I can recreate it correctly. I'm using a flow to set a field to a certain value (01, 02, 03) depending on the value of another field on the same record. I initially wanted to do it with process builder but because of the mapping it seems I would need three 'criteria nodes' or a formula field. Furthermore, it seems Salesforce is recommending using flows instead of process builder for before update actions as it is faster.  The problem with Flows is that I found a way to trigger it when the record is new or updated but not when the specific field is changed so it triggers every time the whole record is updated even when the field stay the same.  On Process Builder, you can use isChanged and then call the flow with specific record but that kinds of defeat the point of using flows for before Update.  So is there a possibility to do the same thing directly in flow ?  Thank you for the help ! Every natural number $n$ can be written as $n=s-t$ with $\omega(s)=\omega(t)$ Can we prove the following statement ?  Let $\omega(m)$ denote the number of all distinct prime factors of a positive integer $m$. Prove that every  natural  number $n$ can  be  written  as $n=s-t$, where $s$ and $t$ are positive integers with $\omega(s)=\omega(t)$, in other words, as the difference of two positive integers with the same number of distinct prime factors.   If $n=1$ , we can choose $\ s=3\ $ and $\ t=2$.  If $n$ is even , we can choose $\ s=2n\ $ and $\ t=n$. "Similar questions" overlaps footer and has no background Java equivalent to PHP's preg_replace_callback Show that $\mathbb{Q}\times \mathbb{Q}$ is denumerable Record a macro of windows commands Using Windows 7, is there an in-built or third-party method of recording windows commands and being able to play them back?  As a very basic example of what I would like to be able to do, imagine having two desktop themes that you like to alternate between. The Windows commands would be something like   Open personalisation applet select second theme ok   (I'm calling this a macro because of the equivalent capability in Word.) Batch script to resize height of all layers to same height but keeping their original aspect ratio I have hundreds of product image layers and I am trying to resize them all to the same height (ignoring the width) and retaining their individual aspect ratio's.  Is there a script available that does this? Or a feature I am unaware of?  Thanks! Why should the interface for a Java class be preferred?