This is a proposal for MPI 2.1, Ballot 4. This is a follow up to: Why no MPI_INPLACE for MPI_EXSCAN? in http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/index.h... with mail discussion in http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/discuss... Bill Gropp has already put a proposal on the web page. I would chang the location: Instead of putting the clarification at the end of the Advice to users, I would add at the beginning of the 2nd paragraph of the Rationale. Proposal for MPI 2.1, Ballot 4: ------------------------------- MPI-2, Sect. 7.3.6, page 167. lines 6-8 read: The reason that MPI-1 chose the inclusive scan is that the definition of behavior on processes zero and one was thought to offer too many complexities in definition, particularly for user-defined operations. (End of rationale.) but should read: No in-place version is specified for MPI_EXSCAN because it isn't clear what this means for the process for rank zero. The reason that MPI-1 chose the inclusive scan is that the definition of behavior on processes zero and one was thought to offer too many complexities in definition, particularly for user-defined operations. (End of rationale.) ------------------------------- Background information: The total rationale On MPI-2 page 167 would be then Rationale. The exclusive scan is more general than the inclusive scan provided in MPI-1 as MPI SCAN. Any inclusive scan operation can be achieved by using the exclusive scan and then locally combining the local contribution. Note that for noninvertable operations such as MPI MAX, the exclusive scan cannot be computed with the inclusive scan. No in-place version is specified for MPI_EXSCAN because it isn't clear what this means for the process for rank zero. The reason that MPI-1 chose the inclusive scan is that the definition of behavior on processes zero and one was thought to offer too many complexities in definition, particularly for user-defined operations. (End of rationale.) Best regards Rolf Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner_at_[hidden] High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)