#include "stdio.h"
#include "mpi.h"
void main(int argc, char *argv[]) 
{
	int mcol, irow, jcol, p;
	MPI_Comm row_comm, col_comm, comm2D;
	int Iam, row_id, col_id;
	int row_group, row_key, map[6];

	/* 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 */

	if (p != 6)
	{
		printf("Use 6 processes to run this program!!\n");
		exit(0);
	}

	map[0]=2; map[1]=1; map[2]=2; map[3]=1; map[4]=0; map[5]=1;
	mcol=2;   /* nrow = 3 */
	if(Iam == 0) {
		printf("\n");
		printf("Example of MPI_Comm_split Usage\n");
		printf("Split 3x2 grid into 2 different communicators\n");
		printf("which correspond to 3 rows and 2 columns.");
		printf("\n");
		printf("     Iam     irow     jcol   row-id   col-id\n");
	}
	/* virtual topology with nrow rows and mcol columns */
	irow = Iam/mcol;        /* row number:		0 0 1 1 2 2 */
	jcol = Iam%mcol;        /* column number:	0 1 0 1 0 1 */
	comm2D = MPI_COMM_WORLD;
	MPI_Comm_split(comm2D, irow, jcol, &row_comm);
	MPI_Comm_split(comm2D, jcol, irow, &col_comm);

	MPI_Comm_rank(row_comm, &row_id);
	MPI_Comm_rank(col_comm, &col_id);
	MPI_Barrier(MPI_COMM_WORLD);

	printf("%8d %8d %8d %8d %8d\n",Iam,irow,jcol,row_id,col_id);
	fflush(stdout);
	MPI_Barrier(MPI_COMM_WORLD);
	sleep(1);

	if(Iam == 0) {
		printf("\n");
		printf("Next, create more general communicator\n");
		printf("which consists of two groups :\n");
		printf("Rows 1 and 2 belongs to group 1 and row 3 is group 2\n");
		printf("\n");
		printf("     Iam new rank\n");
	}
	/* MPI_Comm_split is more general than MPI_Cart_sub
	simple example of 6 processes divided into 2 groups;
	1st 4 belongs to group 1 and remaining two to group 2 */
	row_group = Iam/4;	/* this expression by no means general */
	row_key = Iam - row_group*4;	/* group1:0,1,2,3; group2:0,1 */
	MPI_Comm_split(comm2D, row_group, row_key, &row_comm);
	MPI_Comm_rank(row_comm, &row_id);
	printf("%8d %8d\n",Iam,row_id);
	fflush(stdout);
	MPI_Barrier(MPI_COMM_WORLD);
	sleep(1);

	if(Iam == 0) {
		printf("\n");
		printf("If two processes have same key, the ranks\n");
		printf("of these two processes in the new\n");
		printf("communicator will be ordered according'\n");
		printf("to their order in the old communicator\n");
		printf(" key = map[Iam]; map = (2,1,2,1,0,1)\n");
		printf("     Iam new rank\n");
		printf("\n");
	}
	/* MPI_Comm_split is more general than MPI_Cart_sub
	simple example of 6 processes dirowided into 2 groups;
	1st 4 belongs to group 1 and remaining two to group 2 */
	row_group = Iam/4;     /* this expression by no means general */
	row_key = map[Iam];
	MPI_Comm_split(comm2D, row_group, row_key, &row_comm);
	MPI_Comm_rank(row_comm, &row_id);
	printf("%8d %8d\n",Iam,row_id);
	fflush(stdout);
	MPI_Barrier(MPI_COMM_WORLD);

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