pi3halfdone.c

#include "mpi.h"
#include <math.h>
#include <stdio.h>
#include <omp.h>
 
int main(argc,argv)
int argc;
char *argv[];
{
    int done = 0, n, myid, numprocs, i, len, provided, tid;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x;
    char   pname[MPI_MAX_PROCESSOR_NAME];
     
    MPI_Init_thread(&argc,&argv,MPI_THREAD_FUNNELED,&provided);
    if (provided<MPI_THREAD_FUNNELED) 
    { MPI_Finalize(); return 1; }

    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);

    MPI_Get_processor_name(pname,&len); 
    printf("Process %d of %d is alive on host %s\n",myid,numprocs,pname);


    while (!done)
    {
        if (myid == 0) {
            printf("Enter the number of intervals: (0 quits) ");
            scanf("%d",&n);
        }
        //Work: Broadcast n to all ranks
        if (n == 0) break;
         
        h   = 1.0 / (double) n;
        sum = 0.0;

        //Work: Split the loop over MPI processes
        for (i = 1; i <= n; i ++) {
            //Work: Find out which process runs which iterations
            x = h * ((double)i - 0.5);
            sum += 4.0 / (1.0 + x*x);
        }
        mypi = h * sum;
        
        //Work: Do reduction of partial results into pi 
         
        if (myid == 0)
            printf("pi is approximately %.16f, Error is %.16f\n",
                   pi, fabs(pi - PI25DT));
    }
    MPI_Finalize();
    return 0;
}