Re:
what is exactly meant with "in which all processes contribute to the result and all processes receive the result" - what is "the result"? This doesn't really describe an alltoall, since any process only receives part of a "result". Perhaps this should be reformulated to "in which all processes contribute data and all processes receive data"? This probably doesn't catch MPI_Scan, though.
Or, perhaps it should use the existing terminology in Section 5.2.2 on pages 134-135 of the 2.2 document? This issue is one of the many problems with the proposed changes. They are not consistent with the existing document. It is one of the many examples of how the changes were assembled in a hurried fashion that is not appropriate for something that would become a lasting portion of the standard if accepted. The appropriate thing is for those who proposed this ticket to withdraw it although I harbor no illusions that such actions will occur. Bronis