custom_type_b.c

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

int main(int argc, char **argv)
{
    int rank;
    int array[8][8];
    MPI_Datatype indexedtype;
    int displs[4];
    int counts[4];

    int i, j;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    // Initialize arrays
    if (rank == 0) {
        for (i = 0; i < 8; i++) {
            for (j = 0; j < 8; j++) {
                array[i][j] = (i + 1) * 10 + j + 1;
            }
        }
    } else {
        for (i = 0; i < 8; i++) {
            for (j = 0; j < 8; j++) {
                array[i][j] = 0;
            }
        }
    }

    if (rank == 0) {
        printf("Data in rank 0\n");
        for (i = 0; i < 8; i++) {
            for (j = 0; j < 8; j++) {
                printf("%3d", array[i][j]);
            }
            printf("\n");
        }
    }

    // Create datatype
    for (i = 0; i < 4; i++) {
        counts[i] = i + 1;
        displs[i] = i + 2 * i * 8;
    }

    MPI_Type_indexed(4, counts, displs, MPI_INT, &indexedtype);
    MPI_Type_commit(&indexedtype);

    // Send first indexed of matrix
    if (rank == 0) {
        MPI_Send(array, 1, indexedtype, 1, 1, MPI_COMM_WORLD);
    } else if (rank == 1) {
        MPI_Recv(array, 1, indexedtype, 0, 1, MPI_COMM_WORLD,
                 MPI_STATUS_IGNORE);
    }

    // Print out the result on rank 1
    // The application is correct if the first column has the values of rank 0
    if (rank == 1) {
        printf("Received data\n");
        for (i = 0; i < 8; i++) {
            for (j = 0; j < 8; j++) {
                printf("%3d", array[i][j]);
            }
            printf("\n");
        }
    }

    MPI_Type_free(&indexedtype);
    MPI_Finalize();

    return 0;
}