并行求pi (C++实现)

用OpenMP并行化求pi的代码，这里用的是公式法求pi。具体如下：

//公式法
#include<omp.h>
#include<stdio.h>
#include<stdlib.h>

#define n_threads  2   //这里线程数设为2
static int num_steps = 10000000;  //步数

int main() {
	int i;
	double sum = 0.0;
	double x;
	double pi;
	double factor;
	omp_set_num_threads(n_threads);  //并行化
#pragma omp parallel for reduction(+:sum) private(x, factor)
	for (i = 0;i<num_steps;i++)
	{
		if (i % 2 == 0)
			factor = 1.0;
		else
			factor = -1.0;
		x = factor / (2 * (double)(i)+1);
		sum = sum + x;
	}
	pi = 4 * sum;
	printf("when num_steps is %d pi is: %2.8f\n", num_steps, pi);
	return 0;
}

得到的结果为：3.14159255