zipf算法

#include
#include
#include
#include

#define ALPHA_VALUE 0.73

int zipf_variate(int N, double alpha = ALPHA_VALUE)
{
 double sigma = 0.0;
 double sum = 0.0;
 int i;
 double r = (double)rand() / (double)RAND_MAX * 1.0;
 for(i = 0; i < N; i++)
 {
    sigma += exp(-alpha*log(i+1));
  }
  for(i = 0; i < N; i++)
  {
   sum += exp(-alpha*log(i+1));
   if (sum / sigma >= r)
     return i;
  }
  return i;
}