MPI_Comm_group(commrev, &grev);
MPI_Comm_group(MPI_COMM_SELF, &gself);
MPI_Comm_group(comm, &gworld);
/* sanity check correctness first */
MPI_Comm_group(commrev, &grev);
MPI_Comm_group(MPI_COMM_SELF, &gself);
MPI_Comm_group(comm, &gworld);
/* sanity check correctness first */