The listing of third.c

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include "mpi.h"

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

int main ( int argc, char **argv )
{
    int pool_size, my_rank, host_rank, destination, source, node_name_length,
        *host_rank_ptr, found_flag, int_buffer[BUFSIZ];
    char char_buffer[BUFSIZ], my_node_name[BUFSIZ], console_name[BUFSIZ],
         host_name[BUFSIZ]; 
    MPI_Status status;
    boolean_t i_am_the_master = B_FALSE; 

#include "preamble.c"

    { 
       int n, i;
       double mypi, pi, h, sum, x, a, start_time, end_time,
              communication_time, computation_time;

       while (1) {
          if (i_am_the_master) {
             printf("Enter the number of intervals: (0 quits) ");
             scanf("%d",&n);
          }

          start_time = MPI_Wtime();
          MPI_Bcast(&n, 1, MPI_INT, host_rank, MPI_COMM_WORLD);
          end_time = MPI_Wtime();
          communication_time = end_time - start_time;

          if (n == 0) break;
          else {

             start_time = MPI_Wtime();

             h   = 1.0 / (double) n;
             sum = 0.0;
             for (i = my_rank + 1; i <= n; i += pool_size) {
                x = h * ((double)i - 0.5);
                sum += f(x);
             }
             mypi = h * sum;

             end_time = MPI_Wtime();
             computation_time = end_time - start_time;
      
             start_time = MPI_Wtime();
             MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, host_rank,
                        MPI_COMM_WORLD);
             end_time = MPI_Wtime();
             communication_time = communication_time + end_time - start_time;
      
             if (i_am_the_master) {
                printf("pi is approximately %.16f\n", pi);
                printf("computation time %.16f\n", computation_time);
                printf("communication time %.16f\n", communication_time);
             }
          }
       }
    }

    MPI_Finalize ();
}