[Mpi-22] MPI_INIT_ASSERTED proposal for MPI-2.2

Ashley Pittman apittman at [hidden]
Wed May 21 10:40:58 CDT 2008

On Fri, 2008-05-16 at 14:51 -0400, Richard Treumann wrote:

> The MPI standard either requires or strongly urges that an
> MPI_REDUCE/MPI_ALLREDUCE give exactly the 
> same answer every time. There are applications that do not need a
> "same answer" promise as long as
> they can assume they will get a "correct" answer. Maybe they can be
> provided a faster reduction algorithm.

This makes zero sense as a hint and would make the standard
contradictory if adopted.  I've already made it clear I would prefer
assertions and this option would be useful in that context, if hints
turn out the be chosen over assertions then this flag should be dropped.

Clarification of the standard over the results of floating point
reduction results would probably be a good thing anyway, for example is
it OK for the different communicators of the same size but with
different process layouts to give different answers given the same input
data?  I suspect the standard forbids this although without it it's
probably impossible to do any shared memory optimisations.

Ashley Pittman.

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