On Sep 20, 2011, at 7:52 AM, Tim Prince wrote:
> Quoted comment from OP seem to show a somewhat different question: Does OpenMPI implement any operations in a different way from MVAPICH? I would think it probable that the answer could be affirmative for operations such as allreduce, but this leads well outside my expertise with respect to specific MPI implementations. It isn't out of the question to suspect that such differences might be aggravated when using excessively aggressive ifort options such as -fast.
This is 'zactly what I was going to say -- reductions between Open MPI and MVAPICH may well perform global arithmetic operations in different orders.
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