[MPICH] empty group returned by MPI_Group_excl

[Rajeev Thakur]

It is not spelled out in the definition of MPI_Group_excl, but it is in
others. For example,
MPI_Group_difference: "The new group can be empty, that is, equal to
MPI_GROUP_EMPTY."
MPI_Group_incl: "If n = 0, then newgroup is MPI_GROUP_EMPTY." 
So I would guess that if MPI_Group_excl results in an empty group, one would
expect to get back MPI_GROUP_EMPTY.

Rajeev

> -----Original Message-----
> From: owner-mpich-discuss at mcs.anl.gov 
> [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Toon Knapen
> Sent: Thursday, July 05, 2007 2:50 AM
> To: mpich-discuss at mcs.anl.gov
> Subject: [MPICH] empty group returned by MPI_Group_excl
> 
> Hi all,
> 
> I noticed that there is a test in test/mpi/group/grouptest.c of 
> mpich2-1.0.5p4 that verifies that a group of which all ranks are 
> excluded (using MPI_Group_excl) is equal to MPI_GROUP_EMPTY.
> 
> Is this really required by the standard? AFAICT the standard does not 
> require that an empty group is equal to MPI_GROUP_EMPTY (both 
> groups of 
> course will be MPI_IDENT).
> 
> Thanks in advance,
> 
> Toon Knapen
> 
>