George thinks MPI_DATATYPE_NULL cannot be used even when count=0, which I think is ridiculous, particularly when one makes the analogy to buffer=NULL.

See http://www.open-mpi.org/community/lists/users/2016/01/28255.php for the thread in question.

There is example code in MPI that uses this behavior.  George and I agree that example text is non-normative, but I cannot imagine how this example came to exist without the Forum believing it to be valid.

Jeff
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