[Lemon-devel] Strange running time results

[Alpár Jüttner]

Hi,

I compiled the code you can see below. I used g++-4.1.2 with
optimization flag -O2. The attached picture shows the running times of
the iterations.

Could anyone explain that strange "forking" tendency in the running
times?

Regards,
Alpar

#include <lemon/time_measure.h>
#include <iostream>

double mpower_sum(int size,double *m)
{
  double s=0;
  for(int i=0;i<size;i++)
    for(int j=0;j<size;j++)
      for(int k=0;k<size;k++)
	s+=m[i*size+k]*m[k*size+j];
  return s;
}

int main(int argc,char **argv)
{
  int size=1000;
  int step=10;
  
  double *m = (double *)malloc(sizeof(double)*(size*size+3));
  for(int i=0;i<size*size;i++) m[i]=i;
  for(int i=step;i<=size;i+=step)
    {
      lemon::Timer t;
      mpower_sum(i,m);
      std::cout << i << ' ' << t.realTime() << std::endl;
    }
  free(p);
}

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