int group_union(MPI_Group group2, MPI_Group* newgroup);
int intersection(MPI_Group group2, MPI_Group* newgroup);
int difference(MPI_Group group2, MPI_Group* newgroup);
int group_union(MPI_Group group2, MPI_Group* newgroup);
int intersection(MPI_Group group2, MPI_Group* newgroup);
int difference(MPI_Group group2, MPI_Group* newgroup);