MPI并行计算学习笔记2——圆周率pi的并行求解

调式环境：VS2017 + MPI

圆周率PI的数值计算公式如下：

 

#include<iostream>
#include"mpi.h"
#include<ctime>
#include<cmath>
using namespace std;


const int N = 1000000;
double start,finish;//计算的起止时间
int main(int argc, char* argv[])
{
	MPI_Init(&argc, &argv);//MPI库的初始化
	int numprocs, myid;//定义进程总数及进程标识
	MPI_Comm_size(MPI_COMM_WORLD, &numprocs);//获得进程数
	MPI_Comm_rank(MPI_COMM_WORLD, &myid);//获得当前进程标识号0,1,2,3,....,numprocs - 1
	
        start = MPI_Wtime();//获得时间
	double partSum = 0.0;//定义部分和
	double pi = 0.0;//定义pi的值
	for (int i = myid; i < N; i += numprocs)
	     {
                partSum += sqrt(1 - (double(i) / N)*(double(i) / N)) / N;
              //partSum += sqrt(1.0 - (double)(i * i) / (N * N))/N; int型乘法会有溢出问题
             }
	MPI_Reduce(&partSum, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
       //规约操作，将各进程的partSum发送到0号进程并求和
	
	cout << "我的标识是" << myid << ",求得的partSum值为:" << partSum << endl;
	if (myid == 0)
	{
		pi *= 4.0;
		finish = MPI_Wtime();
		cout << "求得近似的pi值为:" << pi << endl;
		cout<<"调用"<<numprocs<<"个进程的计算时间为:"<< finish - start<< endl;
	}
		
	
	MPI_Finalize();
	//system("pause");
	return 0;
}

 

 

分别调用1，2，3个进程，所得结果：