It is valid. The buffer and type are significant only when the count is non-zero. -- Pavan Sent from my iPhone On Jan 13, 2016, at 11:26 AM, Jeff Hammond <[email protected]<mailto:[email protected]>> wrote: Is it allowed to communicate messages with (buffer=NULL,count=0,type=MPI_DATATYPE_NULL)? 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 -- Jeff Hammond [email protected]<mailto:[email protected]> http://jeffhammond.github.io/ _______________________________________________ mpi-forum mailing list [email protected]<mailto:[email protected]> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum