communicator

A communicator is a collection of processes that can send message to each other.

Example:

#include <stdio.h>
#include <mpi.h>
 
int main(void) {
	int comm_sz, my_rank;
	MPI_Init(NULL, NULL);
	MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
	printf(“hello, world from process %d out of %d\n”, my_rank, comm_sz);
	MPI_Finalize();
	return 0;
}

int MPI_Comm_size(MPI_Comm comm, int* comm_sz_p) takes a communicator and a pointer an integer, which value is set by the function to the number of processes in the communicator.

int MPI_Comm_rank(MPI_Comm comm, int* my_rank_p) takes a communicator and a pointer an integer, which value is set by the function to the rank of the process calling it.

New communicators can be created.