Btukfyl

I wrote a program to calculate y = A*b. and I use MPI_Scatter to scatter the rows of the matrix A among processors and MPI_Gather to collect the calculated data and then print them. I don't know where I went wrong, and why the code prints some non-sense numbers. please help. Thank you.

here is my code:

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include "mpi.h"





int main(int argc, char *argv){



    int m = 8,n = 8, i, j, num = 0;

    int rank, size;



    MPI_Init(&argc, &argv);

    MPI_Comm_size(MPI_COMM_WORLD, &size);

    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    //!Allocating and generating matrix A.

    int *A = (int*) malloc(m * n * sizeof(int));

    if (rank == 0) {

        for (i = 0; i < m; ++i) {

            for (j = 0; j < n; ++j) {

                A[i*n+j] = ++num;

            }

        }

    }

    //Scatter the matrix A into processores

    MPI_Scatter(A, n/size, MPI_INT, A, n/size, MPI_INT, 0, MPI_COMM_WORLD);

    //Allocating and generating vector b.

    int *b = (int*) malloc(n * sizeof(int));

        for (i = 0; i < n; ++i) {

            b[i] = ++num;

        }

    //Allocating the vector y   

    int *y = (int*) calloc (m, sizeof(int));



    //calculation of y.

    for (i = 0; i < m; ++i) {

        for (j = 0; j < n; ++j) {

            y[j] += A[i*n+j] * b[i];



        }

    }

    //collect all data from processors.

    MPI_Gather(&y, 1, MPI_INT, y, 1, MPI_INT, 0, MPI_COMM_WORLD);

    if (rank == 0) {

        for (i = 0; i < n; ++i) {

            printf("%dn", y[i]);

        }

    }

    //free the allocated memory.

    free (A);

    free (b);

    free (y);

    MPI_Finalize();

    return 0;

}