Openmp并行简单算例1

#include <stdio.h>

#include <time.h>

#include <omp.h>


int main(void)
{
  static long num_steps=1000000000;
  double step;
  int i;
  double x,pi,walltime,sum=0.0;
  step=1.0/(double)num_steps;
  omp_set_num_threads(NUM_THREADS);

  time_t start;
  start=time(NULL);

#pragma omp parallel for reduction(+:sum)private(x)
  for(i=0;i<num_steps;i++)< p="">
  {
  x=(i+0.5)*step;
  sum+=4.0/(1.0+x*x);
  }

 pi=sum*step;
  printf("Pi=%21.20f(%d steps)\n",pi,num_steps);

  walltime=time(NULL)-start;
  printf("It cost %f sec",walltime);

  return 0;
}