obliczanie pi z mpi bcast i redce

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

double calka(double x)
{
        return 4.0/ (1 + x * x );
}

int main(int argc, char *argv[])
{
        int id, numproc;
        int i,n, root = 0;
        double pi,h,suma,x;

        MPI_Init(&argc, &argv);
        MPI_Comm_rank(MPI_COMM_WORLD, &id);
        MPI_Comm_size(MPI_COMM_WORLD, &numproc);

        if(id == root)
        {
            printf("Okresl liczba przedzialow: ");
        }
        scanf("%d", &n);

        MPI_Bcast( &n, 1, MPI_INT, root, MPI_COMM_WORLD);
        h = 1.0/(double)n;

        suma = 0.0;
        for ( i = id; i < n; i+=numproc)
        {
            x = h * ((double)i + 0.5);
            suma += 4.0/(1 + x * x);
        }

        MPI_Reduce( &suma, &pi, 1, MPI_DOUBLE, MPI_SUM, root, MPI_COMM_WORLD);

        if ( id == root )
        {
            pi = h * pi;
            printf("pi = %.20f\n", pi);
        }

        MPI_Finalize();
        return 0;
}