MSc_parallel_prog_2025_lab5/mpi_navier.cpp at main · DobDan42/MSc_parallel_prog_2025_lab5 · GitHub

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#include <mpi.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

int my_rank;
int nprocs;
int nprocs_y;
int nprocs_x;
int my_rank_x;
int my_rank_y;
int prev_y;
int next_y;
int next_x;
int prev_x;
int imax_full;
int jmax_full;
int gbl_i_begin;
int gbl_j_begin;
MPI_Comm cartcomm;
MPI_Datatype row, column;

void mpi_setup(int *imax, int *jmax) {
	//Initialise: get #of processes and process id
	 MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
	int dims[2] = {0,0}; int periods[2] = {0,0};
	int reorder = 0;

 	 MPI_Dims_create(nprocs, 2, dims);
	 nprocs_x = dims[0];
	 nprocs_y = dims[1];

    //Create cartesian communicator for 2D, dims[0]*dims[1] processes,
    //without periodicity and reordering
    MPI_Cart_create(MPI_COMM_WORLD, 2, dims, periods, reorder, &cartcomm);

	//Figure out process X,Y coordinates
	MPI_Comm_rank(cartcomm, &my_rank);
    //Get my coordinates coords[0] and coords[1]
	int coords[2];
    MPI_Cart_coords(cartcomm, my_rank, 2, coords);
	my_rank_x = coords[0];
	my_rank_y = coords[1];
	//Figure out neighbours
	//Get my neighbours in dimension 0
    MPI_Cart_shift(cartcomm, 0, 1, &prev_x, &next_x);
    //Get my neighbours in dirmension 1
    MPI_Cart_shift(cartcomm, 1, 1, &prev_y, &next_y);


	//Save original full sizes in x and y directions
	//Modify imax and jmax (pay attention to integer divisions's rounding issues!)
	imax_full = *imax;
	*imax = *imax / nprocs_x;
	if (my_rank_x == nprocs_x -1){
		int remainder = imax_full % nprocs_x;
		*imax = *imax + remainder;
	}
	jmax_full = *jmax;
	*jmax = *jmax / nprocs_y;
	if (my_rank_y == nprocs_y -1){
		int remainder = jmax_full % nprocs_y;
		*jmax = *jmax + remainder;
	}
	//Figure out beginning i and j index in terms of global indexing

	gbl_i_begin = my_rank_x * (imax_full / nprocs_x);
	gbl_j_begin = my_rank_y * (jmax_full / nprocs_y);
	//Let's set up MPI Datatypes
	MPI_Type_vector((*imax+2), 1,1,MPI_DOUBLE, &row);
	MPI_Type_vector((*jmax+2), 1,(*imax+2),MPI_DOUBLE, &column);
	MPI_Type_commit(&row);
	MPI_Type_commit(&column);

}

void exchange_halo(int imax, int jmax, double *arr) {
	//Exchange halos: prev_y, next_y, prev_x, next_x
	MPI_Sendrecv(&arr[1], 1, column, prev_x, 421,
		&arr[imax+1], 1, column,  next_x, 421, cartcomm, MPI_STATUS_IGNORE);
	MPI_Sendrecv(&arr[imax+0], 1, column, next_x, 421,
		&arr[0], 1, column,  prev_x, 421, cartcomm, MPI_STATUS_IGNORE);

	MPI_Sendrecv(&arr[(jmax)*(imax+2)], 1, row, next_y, 421,
		&arr[0], 1, row,  prev_y, 421, cartcomm, MPI_STATUS_IGNORE);
	MPI_Sendrecv(&arr[1*(imax+2)], 1, row, prev_y, 421,
		&arr[(jmax+1)*(imax+2)], 1, row,  next_y, 421, cartcomm, MPI_STATUS_IGNORE);


}