计算PI的两种方法（调试通过）

 

 

/* Seriel Code */

#include

#include

#include

static long num_steps = 500000000;

double step;

int main()

{

int i;

double x, pi, sum = 0.0;

struct timeval start, finish;

double diffsec,diffusec;

gettimeofday(&start,NULL);

step = 1.0/(double) num_steps;

   for (i=0;i< num_steps; i++){

    x = (i+0.5)*step;

    sum = sum + 4.0/(1.0+x*x);

}

pi = step * sum;

    gettimeofday(&finish,NULL);

    diffsec=(double)finish.tv_sec-start.tv_sec;

    diffusec=(double)(finish.tv_usec-start.tv_usec)/(double)1000000;

    diffsec+=diffusec;

    printf("Cost time=%f second ,pi=%20.14lf\n",diffsec,pi);

    return 0;

}

/*parallel program with openmp*/

#include

#include

#include

#include

static long num_steps = 500000000;

double step;

#define NUM_THREADS 2

int main()

{

 int i;

 double x, sum, pi=0.0;

 struct timeval start, finish;

 double diffsec,diffusec;

 gettimeofday(&start,NULL);

 step = 1.0/(double) num_steps;

 omp_set_num_threads(NUM_THREADS);

#pragma omp parallel for private(x)  reduction(+:sum)

     for (i=0;i<= num_steps; i++){

     x = (i+0.5)*step;

     sum = sum + 4.0/(1.0+x*x);

}

    gettimeofday(&finish,NULL);

    diffsec=(double)finish.tv_sec-start.tv_sec;

    diffusec=(double)(finish.tv_usec-start.tv_usec)/(double)1000000;

    diffsec+=diffusec;

    printf("Cost time=%f second ,pi=%20.14lf\n",diffsec,sum/num_steps);

    return 0;

}

编译方法：gcc -fopenmp -o parallel openmp.c