[OMPI users] MPI_Comm_create with unequal group arguments

[Jens Jørgen Mortensen]

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