Write a MPI program to find factorial of given number.

Q. Write a MPI program to find factorial of given number. (MAY 18) 10M

Ans- MPI program to find factorial of a given number

#include <stdio.h>

#include "mpi.h"

int main(int argc, char *argv[]){

    int myRank;

    int size;

    int fact;

    int lower,upper;

    int i;

    double local_result = 1.0;

    double total;

    /* initialize MPI */

    MPI_Init(&argc,&argv);

    /* get my rank and the size of the communicator */

    MPI_Comm_rank(MPI_COMM_WORLD, &myRank);

    MPI_Comm_size(MPI_COMM_WORLD, &size);

    /* get the input. (only if i have rank 0) */

    if(myRank==0){

        printf("Enter a number:");

        scanf("%d",&fact);

    }

    /* since only the process with rank 0 has the input,

     * we must pass it to all the other processes. */

    MPI_Bcast(&fact, /* in/out parameter */

              1,     /* count */

              MPI_INT, /* datatype */

              0,       /* root */

              MPI_COMM_WORLD); /* communicator */

    /* calculate the upper and lower boundaries

     * for each process

     */

    if(myRank==0){

        lower = 1;

    }else

        lower = myRank * (fact / size) + 1;

    if(myRank==(size-1))

        upper = fact;

    else

        upper = (myRank + 1) * (fact / size);

    /* now that we know upper and lower, do the

     * multiplication in our local area

     */

    for(i=lower;i<=upper;i++){

        local_result = local_result * (double)i;

    }

    /* combine all the local results by multiplying them 

     * together

     */

    MPI_Reduce(&local_result, /* operand */

               &total,        /* result */

               1,             /* count */

               MPI_DOUBLE,    /* datatype */

               MPI_PROD,      /* operator */

               0,             /* root rank */

               MPI_COMM_WORLD); /* communicator */

    /* give the output to the user */

    if(myRank==0){

        printf("The factorial of %d is %lf, and was calculated using %d processes\n",fact,total,size);

    }

    /* shut down MPI */

    MPI_Finalize();

    return 0;

}