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

int main(int argc, char* argv[]) 
{
  int p, my_rank, q;
  MPI_Comm  grid_comm;
  int dim_sizes[2];
  int wrap_around[2], coordinates[2], free_coords[2];
  int reorder = 1;
  int my_grid_rank, grid_rank;
  int       row_test, col_test;
  MPI_Comm  row_comm, col_comm;
  
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &p);
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
  
  q = (int) sqrt((double) p);
  
  dim_sizes[0] = dim_sizes[1] = q;
  wrap_around[0] = wrap_around[1] = 1;
  MPI_Cart_create(MPI_COMM_WORLD, 2, dim_sizes, wrap_around, reorder, &grid_comm);
  
  MPI_Comm_rank(grid_comm, &my_grid_rank);
  MPI_Cart_coords(grid_comm, my_grid_rank, 2, coordinates);
  MPI_Cart_rank(grid_comm, coordinates, &grid_rank);
  
  printf("Process %d > my_grid_rank = %d,"
	 "coords = (%d,%d), grid_rank = %d\n",
	 my_rank, my_grid_rank, coordinates[0], 
	 coordinates[1], grid_rank);
  
  free_coords[0] = 0; free_coords[1] = 1;
  
  MPI_Cart_sub(grid_comm, free_coords, &row_comm);
  
  if (coordinates[1] == 0)
    row_test = coordinates[0];
  else
    row_test = -1;
  
  MPI_Bcast(&row_test, 1, MPI_INT, 0, row_comm);
  printf("Process %d > coords = (%d,%d), row_test = %d\n",
         my_rank, coordinates[0], coordinates[1], row_test);
  
  free_coords[0] = 1; free_coords[1] = 0;
  
  MPI_Cart_sub(grid_comm, free_coords, &col_comm);

  if (coordinates[0] == 0)
    col_test = coordinates[1];
  else 
    col_test = -1;
  
  MPI_Bcast(&col_test, 1, MPI_INT, 0, col_comm);

  printf("Process %d > coords = (%d,%d), col_test = %d\n",
         my_rank, coordinates[0], coordinates[1], col_test);
  
  MPI_Finalize();
  return 0;
}