/*
  file: move.c
  compile: cc move.c -lmpi
  run: mpirun -np 4 ./a.out
*/

#include <stdio.h>
#include "mpi.h"
#define N 4
#define M 4
main(int argc, char* argv[]) {

  int  A[M][N] = {{1, 2, 3, 4},
                  {5, 6, 7, 8},
                  {9, 10, 11 ,12},
                  {13, 14, 15, 16}}, local_A[N][M];
  int  X[N] = {1, 2, 3, 4}, local_X[N];
  int  Y[N], local_Y[N];
  int local_m, local_n;
  int i,j;

  int p;
  int myrank;
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &p);
  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

  local_m = M/p;
  local_n = N/p;
      
  MPI_Scatter(A, local_m*N, MPI_INT, local_A,
              local_m*N, MPI_INT, 0, MPI_COMM_WORLD);

  MPI_Scatter(X, local_n, MPI_INT, local_X, local_n, MPI_INT,
              0, MPI_COMM_WORLD);

  MPI_Allgather(local_X, local_n, MPI_INT, X, local_n, MPI_INT, 
                MPI_COMM_WORLD);

  for (i = 0; i < local_m; i++) {
    local_Y[i] = 0;
    for (j = 0; j < N; j++)
      local_Y[i] = local_Y[i] + local_A[i][j]*X[j];
  }

  MPI_Gather(local_Y, local_m, MPI_INT, Y, local_m, MPI_INT, 0,
             MPI_COMM_WORLD);

  if (myrank == 0){
    for (i=0; i<M; i++) printf("%d ", Y[i]);
    printf("\n");
  }
	
  MPI_Finalize();

}