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

int main(int argc, char *argv[]) { 
    int n, myid, numprocs, i; 
    double PI25DT = 3.141592653589793238462643; 
    double mypi, pi, h, sum, x;
 
    MPI_Init(&argc, &argv); 
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs); 
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
 
    while(1) {
        if(myid == 0) {
            printf("Enter the number of intervals: (0 quits) ");
            scanf("%d", &n);
        }
        MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
        if(n == 0) {
            break;
        }
        else {
            h   = 1.0 / (double)n;
            sum = 0.0;
            for(i=myid+1; i<=n; i+=numprocs) {
                x = h * ((double)i - 0.5);
                sum += (4.0 / (1.0 + x*x));
            }
            mypi = h * sum; 
            MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
            if(myid == 0) {
                printf("pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT));
            }
        }
    }
    MPI_Finalize();
    return 0;
}