On 20-01-2012 15:26, Josh Hursey wrote:
That behavior is permitted by the MPI 2.2 standard. It seems
that our documentation is incorrect in this regard. I'll file a
bug to fix it.
Just to clarify, in the MPI 2.2 standard in Section 6.4.2
(Communicator Constructors) under MPI_Comm_create it states:
"Each process must call with a group argument that is a
subgroup of the group associated with comm; this could be
MPI_GROUP_EMPTY. The processes may specify different values for
the group argument. If a process calls with a non-empty group
then all processes in that group must call the function with the
same group as argument, that is the same processes in the same
order. Otherwise the call is erroneous."
Thanks for reporting the man page bug.
Thanks for the quick reply.
Is it also allowed to call MPI_Comm_create only on those processes
that are in the sub-group? This seems to work also. Or must one
always call MPI_Comm_create on all processes in comm - as the
2012/1/20 Jens Jørgen Mortensen <email@example.com>
For a long time, I have been calling MPI_Comm_create(comm,
group, newcomm) with different values for group on the
different processes of comm. In pseudo-code, I would create
two sub-communicators from a world with 4 ranks like this:
if world.rank < 2:
comm = world.create([0, 1])
comm = world.create([2, 3])
Now I read from the MPI_Comm_create description that this way
of calling MPI_Comm_create is erroneous:
"The call is erroneous if not all group arguments have the
So, I guess I have just been lucky that it has worked for me?
Or is it OK to do what I do?
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Oak Ridge National Laboratory