pi02.c

并行计算的演示程序

#include <omp.h>
static long num_steps = 100000;
double step; 
#define NUM_THREADS 4 
void main () 
{	  int i; 	  
	  double x, pi, sum[NUM_THREADS]; 
	  step = 1.0/(double) num_steps; 
	  omp_set_num_threads(NUM_THREADS); 
	 #pragma omp parallel 
	 {	  
		double x;     
		int id; 
	  	id = omp_get_thread_num(); 
	  	for (i=id, sum[id]=0.0;i< num_steps; i=i+NUM_THREADS){ 
		  	x = (i+0.5)*step; 
		  	sum[id] += 4.0/(1.0+x*x); 
	  	} 
	 } 
	  for(i=0, pi=0.0;i<NUM_THREADS;i++)pi += sum[i] * step; 
	  printf("Pi = %lf\n",pi);
}