• popgen (46/46) Apr 08 2018 I am trying to implement some code to calculate Stirling numbers.
• ag0aep6g (7/17) Apr 08 2018 [...]
• popgen (3/15) Apr 10 2018 Thank you for your help! And I learned two things, the error in

popgen <codequestion mailinator.com> writes:

I am trying to implement some code to calculate Stirling numbers. 
  The code shown below provides the correct calculation but throws 
a Segmentation fault: 11 once it is done running. I suspect there 
is something with the way I am setting up the multidimensional 
array.



import std.stdio;
import std.datetime ;
import std.conv ;
import std.file;
import std.string;
import std.regex;
import std.bigint ;
import std.range : enumerate;


int stirling1(int n, int k)
{
         auto matrix = new int[][](n+1,k+1) ;
         for(int i = 0; i <= n; i++)
         {
             matrix[i][0] = 0 ;
         }
         for(int i = 0; i <= k; i++)
         {
             matrix[0][k] = 0 ;
         }
         for(int i = 1; i <= n ; i++)
         {
             for(int q = 1; q <= i ; q++)
             {
                 if(q == 1 || i == q)
                 {
                     matrix[i][q] = 1 ;
                 }
                 else
                 {
                     matrix[i][q] = q*matrix[i-1][q] + 
matrix[i-1][q-1] ;
                 }
             }
         }
         return(matrix[n][k]) ;
}

void main()
{
     writeln("s(n,k) for s(7,2)") ;
     writeln(stirling1(7,2)) ;
}

ag0aep6g <anonymous example.com> writes:

On 04/08/2018 06:15 PM, popgen wrote:
 I am trying to implement some code to calculate Stirling numbers.  The 
 code shown below provides the correct calculation but throws a 
 Segmentation fault: 11 once it is done running. I suspect there is 
 something with the way I am setting up the multidimensional array.

[...]
 int stirling1(int n, int k)
 {
          auto matrix = new int[][](n+1,k+1) ;

[...]
          for(int i = 1; i <= n ; i++)
          {
              for(int q = 1; q <= i ; q++)

Should it be `q <= k` here? You're using q as an index into an array of 
length k + 1. If you go up to i, you'll exceed that and go out of bounds.

That you're seeing a segfault instead of a range error indicates that 
you're compiling with -release. Better not do that when debugging.

popgen <codequestion mailinator.com> writes:

On Sunday, 8 April 2018 at 16:51:14 UTC, ag0aep6g wrote:
 On 04/08/2018 06:15 PM, popgen wrote:
 [...]

 [...]
  [...]

 [...]
  [...]

 Should it be `q <= k` here? You're using q as an index into an 
 array of length k + 1. If you go up to i, you'll exceed that 
 and go out of bounds.

 That you're seeing a segfault instead of a range error 
 indicates that you're compiling with -release. Better not do 
 that when debugging.

Thank you for your help! And I learned two things, the error in 
the code and not to use -release while debugging.