gistfile1.cpp

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

int main( int argc, char *argv[])
{
    int n, i, k;
    double PI25DT = 3.141592653589793238462643;
    double pi, h, sum, x, recv_sum;

    int numprocs, myid;
    double startTime, endTime;
    MPI_Status stat;

    /* Initialize MPI and get number of processes and my number or rank*/
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);

    /* Processor zero sets the number of intervals and starts its clock*/
    if (myid==0)
    {
        n=100000000 * numprocs;
        startTime=MPI_Wtime();

        for (k = 1; k < numprocs; k++) {
            MPI_Send(&n, 1, MPI_INT, k, k, MPI_COMM_WORLD);
        }
    } else {
        MPI_Recv(&n, 1, MPI_INT, 0, myid, MPI_COMM_WORLD, &stat);
    }

    /* Calculate the width of intervals */
    h   = 1.0 / (double) n;

    /* Initialize sum */
    sum = 0.0;
    /* Step over each inteval I own */
    for (i = myid+1; i <= n; i += numprocs)
    {
            /* Calculate midpoint of interval */
            x = h * ((double)i - 0.5);
            /* Add rectangle's area = height*width = f(x)*h */
            sum += (4.0/(1.0+x*x))*h;
    }
    /* Get sum total on processor zero */
    if (myid == 0) {
        pi = sum;
        for (k = 1; k < numprocs; k++) {
            MPI_Recv(&recv_sum, 1, MPI_DOUBLE, k, k, MPI_COMM_WORLD, &stat);
            pi += recv_sum;
        }
    } else {
        MPI_Send(&sum, 1, MPI_DOUBLE, 0, myid, MPI_COMM_WORLD);
    }

    /* Print approximate value of pi and runtime*/
    if (myid==0)
    {
       printf("pi is approximately %.16f, Error is %e\n",
                       pi, fabs(pi - PI25DT));
       endTime=MPI_Wtime();
       printf("runtime is=%.16f",endTime-startTime);
    }
    MPI_Finalize();
    return 0;
}

[mkelly01@blueshark mod_100m]$ cd ../mod
[mkelly01@blueshark mod]$ cat pcpi.c
#include "mpi.h"
#include <stdio.h>
#include <math.h>

int main( int argc, char *argv[])
{
    int n, i, k;
    double PI25DT = 3.141592653589793238462643;
    double pi, h, sum, x, recv_sum;

    int numprocs, myid;
    double startTime, endTime;
    MPI_Status stat;

    /* Initialize MPI and get number of processes and my number or rank*/
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);

    /* Processor zero sets the number of intervals and starts its clock*/
    if (myid==0)
    {
        n=600000000;
        startTime=MPI_Wtime();

        for (k = 1; k < numprocs; k++) {
            MPI_Send(&n, 1, MPI_INT, k, k, MPI_COMM_WORLD);
        }
    } else {
        MPI_Recv(&n, 1, MPI_INT, 0, myid, MPI_COMM_WORLD, &stat);
    }

    /* Calculate the width of intervals */
    h   = 1.0 / (double) n;

    /* Initialize sum */
    sum = 0.0;
    /* Step over each inteval I own */
    for (i = myid+1; i <= n; i += numprocs)
    {
            /* Calculate midpoint of interval */
            x = h * ((double)i - 0.5);
            /* Add rectangle's area = height*width = f(x)*h */
            sum += (4.0/(1.0+x*x))*h;
    }
    /* Get sum total on processor zero */
    if (myid == 0) {
        pi = sum;
        for (k = 1; k < numprocs; k++) {
            MPI_Recv(&recv_sum, 1, MPI_DOUBLE, k, k, MPI_COMM_WORLD, &stat);
            pi += recv_sum;
        }
    } else {
        MPI_Send(&sum, 1, MPI_DOUBLE, 0, myid, MPI_COMM_WORLD);
    }

    /* Print approximate value of pi and runtime*/
    if (myid==0)
    {
       printf("pi is approximately %.16f, Error is %e\n",
                       pi, fabs(pi - PI25DT));
       endTime=MPI_Wtime();
       printf("runtime is=%.16f",endTime-startTime);
    }
    MPI_Finalize();
    return 0;
}