mpi1

#include <stdio.h>
#include <mpi.h>
 
int main(int argc, char **argv)
{
    double precision = 1000000000;
    int myrank, proccount;
    double pi, pi_final;
    int mine, sign;
    int i;

    // Initialize MPI
    MPI_Init(&argc, &argv);

    // find out my rank
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

    // find out the number of processes in MPI_COMM_WORLD
    MPI_Comm_size(MPI_COMM_WORLD, &proccount);

    // now distribute the required precision
    if (precision < proccount) {
        printf("Precision smaller than the number of processes - try again.");
        MPI_Finalize();
        return -1;
    }
  
    // each process performs computations on its part
    pi = 0;

    int count = precision / proccount;
    if(myrank == proccount - 1) {
        count += precision % proccount;
    }
    mine = count * myrank * 2 + 1;
    sign = (((mine - 1) / 2) % 2) ? -1 : 1;

    for(i = 0; i < count; ++i) {
        pi += sign / (double)mine;
        mine += 2;
        sign = (((mine - 1) / 2) % 2) ? -1 : 1;
    }

    // now merge the numbers to rank 0
    MPI_Reduce(&pi, &pi_final, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

    if (!myrank) {
        pi_final *= 4;
        printf("pi=%f", pi_final);
    }

    // Shut down MPI
    MPI_Finalize();
    return 0;
}