mar11-pi2.c

#include <stdio.h>
#include <math.h>
#include <mpi.h>
#include "l17.h"

#define CIRCLE(step, i) sqrt(4.0 - (double) (i) * (step) * (double) (i) * (step))

int main(int argc, char** argv) {
    int rc;
    rc = MPI_Init(&argc, &argv);
    L17_CHECK_ERROR(MPI_Init, rc);

    int size;
    rc = MPI_Comm_size(MPI_COMM_WORLD, &size);
    L17_CHECK_ERROR(MPI_Comm_size, rc);

    int rank;
    rc = MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    L17_CHECK_ERROR(MPI_Comm_rank, rc);

    if (rank == 0) {
        int N;
        FILE* datp = fopen("mar11-pi2.dat", "r");
        if (datp == NULL) {
            printf("Error. Can't open the data file.\n");
            MPI_Abort(MPI_COMM_WORLD, 1);
        }
        rc = fscanf(datp, "%d", &N);
        if (rc != 1) {
            printf("Error. Can't read the N from the data file.\n");
            MPI_Abort(MPI_COMM_WORLD, 2);
        }
        fclose(datp);

        int i;
        for (i = 1; i < size; ++i) {
            rc = MPI_Send(&N, 1, MPI_INT, i, 1, MPI_COMM_WORLD);
            L17_CHECK_ERROR(MPI_Send, rc);
        }

        double step = 2.0 / (double) N;
        double S_no_coef, FS_no_coef = 0;
        int k = size - 1;
        int j;
        for (j = 0; j < k; ++j) {
            rc = MPI_Recv(&S_no_coef, 1, MPI_DOUBLE, j + 1, 1, MPI_COMM_WORLD, NULL);
            L17_CHECK_ERROR(MPI_Recv, rc);

            FS_no_coef += S_no_coef;
        }

        double coef = step / 2.0;
        double FS = FS_no_coef * coef;

        printf("Pi = %f\n", FS);
    }
    else {
        int j = rank - 1, k = size - 1, ibeg, iend;

        int N;
        rc = MPI_Recv(&N, 1, MPI_INT, 0, 1, MPI_COMM_WORLD, NULL);
        L17_CHECK_ERROR(MPI_Recv, rc);

        ibeg = (N / k) * j;

        iend = (j == k - 1) ? (N - 1) : ((N / k) * (j + 1) - 1);

        double step = 2.0 / (double) N;
        double f_old = CIRCLE(step, ibeg);
        double f_new;
        double S_no_coef = 0;
        int i;
        for (i = ibeg; i <= iend; ++i) {
            f_new = CIRCLE(step, i + 1);
            S_no_coef += f_old;
            S_no_coef += f_new;
            f_old = f_new;
        }

        rc = MPI_Send(&S_no_coef, 1, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD);
        L17_CHECK_ERROR(MPI_Send, rc);
    }

    MPI_Finalize();

    return 0;
}