Grid Subsections

MPI_Comm row_comm;

free_coords[0] = 0;

free_coords[1] = 1;

MPI_Cart_sub(grid_comm, free_coords, &row_comm);

int free_coords[2];

MPI_Comm col_comm;

free_coords[0] = 1;

free_coords[1] = 0;

MPI_Cart_sub(grid_comm, free_coords, &col_comm);