#include "stdio.h"
#include "mpi.h"

/* prototyping ...  */
void foo(int Iam, MPI_Comm comm);

int i, me, ndim, dims[10], coords[10], periods[10];

void main(int argc, char *argv[]) 
{
	int nrow, mcol;
	int p, Iam, me, ndim;
	int coords[2], dims[2];
	int periods[2], belongs[2], reorder;
	MPI_Comm col_comm, grid_comm;

	/* Starts MPI processes ... */
	MPI_Init(&argc, &argv);					/* starts MPI */
	MPI_Comm_rank(MPI_COMM_WORLD, &Iam);	/* get current process id */
	MPI_Comm_size(MPI_COMM_WORLD, &p);		/* get number of processes */

	nrow = 3; mcol = 2; ndim = 2;
	periods[0] = 0; periods[1] = 0; reorder = 1;

	/* create cartesian topology for processes */
	dims[0] = nrow;	/* number of rows */
	dims[1] = mcol;	/* number of columns */
	MPI_Cart_create(MPI_COMM_WORLD, ndim, dims, periods, reorder, &grid_comm);
	MPI_Comm_rank(grid_comm, &me);
	MPI_Cart_coords(grid_comm, me, ndim, coords);

	/* create column subgrids */
	belongs[0] = 1;	/* index belongs to grid - true */
	belongs[1] = 0;	/* index belongs to grid - false */
	MPI_Cart_sub(grid_comm, belongs, &col_comm);

	foo(Iam, col_comm);

	MPI_Finalize();	/* let MPI finish up ...  */
}

void foo(int Iam, MPI_Comm comm)
{
	int i, me, ndim, dims[10], coords[10], periods[10];
	/* Retrieve subgrid dimensions and other info */
	MPI_Cartdim_get(comm, &ndim);
	MPI_Cart_get(comm, ndim, dims, periods, coords);
	MPI_Cart_rank(comm, coords, &me);

	printf("Iam = %2d  ; subgrid rank =  %2d ; subgrid coords =  ",Iam,me);
	for (i=0; i<ndim; i++) {
		printf("%2d",coords[i]);
	}
	printf(" Dimensions of subgrid = %5d\n",ndim);
	printf(" dims :");
	for (i=0; i<ndim; i++) {
		printf("%5d",dims[i]);
	}
	printf(" periods :");
	for (i=0; i<ndim; i++) {
		printf("%5d",periods[i]);
	}
}