Hilfesystem für den Message Passing Interface Standard MPI

/* Wählt die Prozesse 1, 2, 4 und 5 aus und bildet aus ihnen einen 
 * neuen Kommunikator /* 

#include "mpi.h"
#include <stdio.h>
#define MAX 4

int main(int argc, char *argv[]) {

    int                comm_me, newcomm_me, numprocs, n;
    MPI_Comm           newcomm;
    MPI_Group          group, newgroup;
    int                ranks[MAX];

    if (MPI_Init(&argc, &argv)!=MPI_SUCCESS) {
        fprintf( stderr,"MPI_Init failed.\n");
    }
    MPI_Comm_rank(MPI_COMM_WORLD, &comm_me);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    if (numprocs<6) {
	fprintf(stderr,"Program needs at least 6 processes.\n");
	MPI_Finalize();
	return -1;
    }
    MPI_Comm_group(MPI_COMM_WORLD, &group);
    ranks[0]=1;  
    ranks[1]=2;  
    ranks[2]=4;  
    ranks[3]=5;  
    n=MAX;
    MPI_Group_incl(group, n, ranks, &newgroup);
    MPI_Comm_create(MPI_COMM_WORLD, newgroup, &newcomm);

    if (newcomm!=MPI_COMM_NULL) {
        MPI_Comm_rank(newcomm, &newcomm_me);
        fprintf(stderr,"Proc %d: in newcomm %d\n", comm_me,
	        newcomm_me);
	MPI_Barrier(newcomm);
        MPI_Comm_free(&newcomm);
    }

    MPI_Group_free(&newgroup);
    MPI_Finalize();
}