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Subject: [OMPI users] MPI_Comm_create with unequal group arguments
From: Jens Jørgen Mortensen (jensj_at_[hidden])
Date: 2012-01-20 09:00:39


Hi!

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])
else:
     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 same value"

   http://www.open-mpi.org/doc/v1.4/man3/MPI_Comm_create.3.php#toc7

So, I guess I have just been lucky that it has worked for me? Or is it
OK to do what I do?

Jens Jørgen