#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <mpi.h>

// This program show the organisation and use of the Cartesian topology

int main(int argc, char** argv) 
{
	int rank, nb_mpi_processes, ierror, tag, n,i,niter;
	char charbuff[4]; 
	int ndim = 1;                 // number of dimmensions of cartesian topology
	int nb_process_axe[1];        // number of processes per axe of cartesian topology
	int cart_boundaries[1];       // cart_boundaries, type of boundaries : 1 -> periodic, 0 -> non periodic
	int cart_position[1], pos[1]; // position of process on the cartesian topology ( and pos a buffer )
	int cart_neigh[3];            // neigbours rank on the cartesian topology
 
	// CART program
	// This program show the organisation and use of the Cartesian topology

	MPI_Init(NULL, NULL);
	MPI_Comm_size( MPI_COMM_WORLD , &nb_mpi_processes );
	MPI_Comm_rank( MPI_COMM_WORLD , &rank );

	if(nb_mpi_processes != 4) { printf("This program is design to be run with 4 processes only"); return 0;}

	nb_process_axe[0] = 4;
	cart_boundaries[0] = 0;

	MPI_Comm MPI_COMM_CART; // our new communicator

	MPI_Cart_create( MPI_COMM_WORLD , ndim , &nb_process_axe[0] , &cart_boundaries[0] , 1 , &MPI_COMM_CART );

	MPI_Cart_coords( MPI_COMM_CART , rank , ndim , &cart_position[0] );

	MPI_Cart_shift (MPI_COMM_CART, 0, 1, &cart_neigh[0], &cart_neigh[2] );

	printf("Good way to get neigh, Rank : %d Position : %d Neighbours : %d %d\n",rank,cart_position[0],cart_neigh[0],cart_neigh[2]);

	for(i=0;i<=2;i++)
	{
		if((cart_boundaries[0] == 0) && ((cart_position[0] == 0 && i==0) || (cart_position[0] == nb_process_axe[0]-1) && i==2))
		{
			cart_neigh[i] = MPI_PROC_NULL;
		}
		else
		{
			pos[0] = cart_position[0] + i - 1;
			MPI_Cart_rank( MPI_COMM_CART , &pos[0] , &cart_neigh[i] );
		}
	}

	printf("2nd way to get neigh, Rank : %d Position : %d Neighbours : %d %d\n",rank,cart_position[0],cart_neigh[0],cart_neigh[2]);

	MPI_Finalize ( ); // Close MPI

	return 0;
}