[MPICH] empty group returned by MPI_Group_excl

[Toon Knapen]

so do you advise that I'll mention this on the mpi-forum ml?

toon


William Gropp wrote:
> This is a good point, and one that deserves an errata item in the 
> standard.  I would argue that for internal consistency, MPI_GROUP_EMPTY 
> was intended by the Forum, and this case was overlooked.
> 
> Bill
> 
> On Jul 5, 2007, at 3:25 PM, Toon Knapen wrote:
> 
>> Indeed it makes sense that if Group_excl returns an empty group that 
>> it returns MPI_GROUP_EMPTY and of course nothing in the standard 
>> forbids this.
>>
>> But because you test explicitly on this, I just wanted to know if this 
>> is standard-required or an mpich2-convention.
>>
>> thanks,
>>
>> toon
>>
>> Rajeev Thakur wrote:
>>> 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
>>>>
>>>>
>>
>