[mpi-21] Ballot 4 - RE: clarification text for MPI_Reduce_scatter

[Rajeev Thakur]

The only change needed here is that the following sentence on ln 19, pg 163,
MPI 2.0 should be deleted: "Note that the area occupied by the input data
may be either longer or shorter than the data filled by the output data."
The sentence makes no sense because the input data can never be shorter than
the output data. The output, determined by recvcounts[i], is a subset of the
input.

Rajeev

> -----Original Message-----
> From: Rolf Rabenseifner [mailto:rabenseifner_at_[hidden]] 
> Sent: Tuesday, January 29, 2008 4:44 AM
> To: mpi-21_at_[hidden]
> Cc: Rajeev Thakur
> Subject: Ballot 4 - RE: clarification text for MPI_Reduce_scatter
> 
> This is a follow-up for MPI 2.1, Ballot 4.
> 
> I'm asking especially 
>   Rajeev Thakur,
> the participant of the email-discussion in 2002, to review 
> this proposal.
> 
> I would finish the following track without any proposed 
> clarification, because the text is already clear when the MPI-1.1
> part of MPI_Reduce_scatter is put in front of the MPI-2.0 part,
> i.e., in the upcoming combined document MPI-2.1.
> 
> This is a follow up to:
>   MPI_IN_PLACE for MPI_Reduce_scatter 
>   in 
> http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
> errata/index.html
> with mail discussion in
>   
> http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
> errata/discuss/redscat/
> ___________________________________
> 
> The currently text in 
> http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
> errata/index.html
> should not be accepted, because it is a significant modification of
> the MPI-2.0 standard and would break user code:
>   
>    Proposed text to replace lines 16-20, pg 163 
>    The "in place" option for intracommunicators is specified by 
>    passing MPI_IN_PLACE in the sendbuf argument. In this case, on 
>    each process, the input data is taken from recvbuf. Process i gets 
>    the ith segment of the result, and it is stored at the location
>    corresponding to segment i in recvbuf. 
> ___________________________________
> 
> 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)
> 
>