From: Toon Knapen <toon.knapen@XXXXXX>
Date: July 5, 2007 3:25:28 PM CDT
To: Rajeev Thakur <thakur@XXXXXXXXXXX>
Cc: mpich-discuss@XXXXXXXXXXX
Subject: Re: [MPICH] empty group returned by MPI_Group_excl

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@XXXXXXXXXXX [mailto:owner-mpich- 
>> discuss@XXXXXXXXXXXX On Behalf Of Toon Knapen
>> Sent: Thursday, July 05, 2007 2:50 AM
>> To: mpich-discuss@XXXXXXXXXXX
>> 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
>>
>>