#include <stdio.h>
#include <mpi.h>
#define FALSE 0
#define TRUE  1
#define MASTER_RANK 0
 
double f(a)
double a;
{
   return (4.0 / (1.0 + a*a));
}
 
int main ( int argc, char **argv )
{
   int n, i, pool_size, my_rank, i_am_the_master = FALSE;
   double mypi, pi, h, sum, x, a;
 
   MPI_Init(&argc, &argv);
   MPI_Comm_size(MPI_COMM_WORLD, &pool_size);
   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

   if (my_rank == MASTER_RANK) i_am_the_master = TRUE;

   if (i_am_the_master) {
      printf("Enter the number of intervals: ");
      scanf("%d",&n);
      if (n==0) n=100;
   }
 
   MPI_Bcast(&n, 1, MPI_INT, MASTER_RANK, MPI_COMM_WORLD);
 
   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;
 
   MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, MASTER_RANK,
              MPI_COMM_WORLD);
 
   if (i_am_the_master) printf("\npi is approximately %.16f\n", pi);
 
   MPI_Finalize ();
}