Hilfesystem für den Message Passing Interface Standard MPI

für das Splitten eines Kommunikators in zwei gleichstarke und die Kommunikation über einen Intercommunikator

#include "mpi.h"
#include <stdio.h>

#define NUMGROUPS   2
#define TAG         99
#define LEADER_EVEN 0  /* ids der Leader-Procs innerhalb des */
#define LEADER_ODD  1  /* Parent-Communicator MPI_COMM_WORLD */
#define ROOT        0

int main(int argc, char *argv[]) {
    int           me, newid, numprocs, groupsize, color, msg;
    int           local_leader, remote_leader;
    MPI_Status    stat;
    MPI_Comm      newcomm, intercomm;

    if (MPI_Init(&argc, &argv)!=MPI_SUCCESS) {
	fprintf(stderr,"MPI_Init failed.\n");
	return -1;
    }
    MPI_Comm_rank(MPI_COMM_WORLD, &me);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    color=me%NUMGROUPS;
    if ((me==numprocs-1)&&(color!=1)) {
    /* Die Prozeßgruppen sollen gleichstark sein */
	color=MPI_UNDEFINED;
    }
    MPI_Comm_split(MPI_COMM_WORLD, color, me, &newcomm);
    if (color!=MPI_UNDEFINED) {
        MPI_Comm_rank(newcomm, &newid);
        MPI_Comm_size(newcomm, &groupsize);
        fprintf(stderr,"Proc %d: I'm now number %d in a group of %d.\n",
	        me, newid, groupsize);
	MPI_Barrier(newcomm);
	if (color==0) {
	    remote_leader=LEADER_ODD;
	}
	else {
	    remote_leader=LEADER_EVEN;
	}
	MPI_Intercomm_create(newcomm, ROOT, MPI_COMM_WORLD,
			     remote_leader, TAG, &intercomm);
	if (color==0) {
	    msg=me;
	    /* msg an den Partnerprozeß in der anderen Gruppe */
	    MPI_Send(&msg,1,MPI_INT,newid,0,intercomm);
	    fprintf(stderr,"Proc %d: Sending %d to partner.\n", me, msg);
	}
	else {
	    MPI_Recv(&msg,1,MPI_INT,newid,MPI_ANY_TAG,intercomm,&stat);
	    fprintf(stderr,"Proc %d: Received %d from %d (tag %d)\n",
		    me, msg, stat.MPI_SOURCE, stat.MPI_TAG);
	    /*  stat.MPI_SOURCE enthaelt die ID de Senders in */
	    /* dessen lokalen Kommunikator (newcom)           */
	}
	MPI_Comm_free(&intercomm);
	MPI_Comm_free(&newcomm);
    }
    else {
	fprintf(stderr,"Proc %d: I'm in no group.\n", me);
    }
    MPI_Finalize();
}