1.cpp

基于MPI1.2.5并行环境的求PI的VC源代码

#include "mpi.h"
#include <stdio.h>
#include <math.h>

double f(double a)
{
    return (4.0 / (1.0 + a*a));
}

void main(int argc, char *argv[])
{
    int done = 0, n, myid, numprocs, i;  //myid,numprocs分别用来记录某一个并行执行进程的标识和所有参加计算的进程的个数
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x;
    double startwtime, endwtime;
    int  namelen;                       //实际得到的机器名字的长度
    char processor_name[MPI_MAX_PROCESSOR_NAME];     //调用到的机器名
	
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);         //通信域包括的所有进程个数
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);             //调用进程在COMM中的标识号
    MPI_Get_processor_name(processor_name,&namelen);  //得到本进程运行的机器的名称，结果放在
                                                      //processor_name,该字符串的长度放在namelen中 	
    fprintf(stderr,"Process %d on %s\n",             //由于各进程是并行执行的，所以每个进程都会执行下面的语句
		myid, processor_name);
	fflush(stderr);
	
    n = 0;                    //n是0－1区域内被分成的份数
    while (!done)             //done退出标志，如果n取0,done取1，退出该循环
    {
        if (myid == 0)         //将n的值赋给第0进程
        {
	    printf("Enter the number of intervals: (0 quits) ");fflush(stdout);
	    scanf("%d",&n);
	    
	    startwtime = MPI_Wtime();
        }
        MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);   //&n将被广播出去的数据的地址

        if (n == 0)
            done = 1;
        else
        {
            h   = 1.0 / (double) n;
            sum = 0.0;
            for (i = myid + 1; i <= n; i += numprocs)
            {
                x = h * ((double)i - 0.5);
                sum += f(x);
            }
            mypi = h * sum;
			
            MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD); //规约操作，将所有进程的&mypi地址下的数用规约操作符MPI_SUM，求和后赋给0进程的&pi地址
			
            if (myid == 0)
	    {
                printf("pi is approximately %.16f, Error is %.16f\n",
		    pi, fabs(pi - PI25DT));
		endwtime = MPI_Wtime();
		printf("wall clock time = %f\n", endwtime-startwtime);	       
	    }
        }
    }
    MPI_Finalize();
}