[Mpi-forum] Sparse / neighborhood topology ticket 258

[William Gropp]

I also vote for variant A.

Bill

On Feb 9, 2011, at 6:10 AM, Rolf Rabenseifner wrote:

> Dear all,
>
> please make a straw-vote-decision TODAY about the two variants
> in this email. I myself prefer variant A.
>
> The current text does not include a precise definition of the
> sequence of the neighbors.
> I recommend to add such a definition before the Rationale in Sect.  
> 7.6.
>
> New text:
> The sequence of the neighbors is defined
> - in a Cartesian topology by the order of the dimensions,
>   and in each dimension, first the neighbor in the negative
>   direction and then in the positive direction with displacement 1.
>   If such a neighbor does not exist, i.e., at the border
>   in the case of a non-periodic virtual grid dimension
>   (i.e., periods[...]==false), then
>   (VARIANT A)
>   this neighbor is MPI_PROC_NULL and it is still part of the
>   sequence of neighbors, but the corresponding buffer portion
>   is not communicated. The values of indegree and outdegree
>   in the communication routines are 2*ndims with ndims defined
>   defined in MPI_CART_CREATE.
>   (VARIANT B)
>   this neighbor is not part of the sequence of neighbors.
>   The values of indegree and outdegree
>   in the communication routines are 2*ndims (with ndims defined
>   defined in MPI_CART_CREATE), reduced by the number of
>   non-existing neighbors.
>   (END OF VARIANTS)
>   The sequence of incoming and outgoing neighbors is identical.
> - in a general graph topology, the sequence of neighbors
>   in each process is defined through the list of neighbors
>   for this process as defined in the arguments index and edges
>   in MPI_GRAPH_CREATE, which is identical to the sequence
>   returned by MPI_GRAPH_NEIGHBORS.
>   The values of indegree and outdegree in the communication
>   routines are identical to nneighbors returned by
>   MPI_GRAPH_NEIGHBOR_COUNT in each process for its own rank.
>   The sequence of incoming and outgoing neighbors is identical.
> - in a distributed graph topology, the sequence of neighbors
>   in each process is returned by MPI_DIST_GRAPH_NEIGHBORS.
>   The values of indegree and outdegree in the communication
>   routines are identical to the values returned by
>   MPI_DIST_GRAPH_NEIGHBORS_COUNT.
>   If the distributed graph topology was created by
>   MPI_DIST_GRAPH_CREATE_ADJACENT, then the sequence
>   of incoming and outgoing neighbors is
>   identical to the sequence that was defined in
>   MPI_DIST_GRAPH_CREATE_ADJACENT.
>
> With this detailled definition, the following remark in parentheses
> in 7.6.1 and 7.6.2 can be removed:
>   (the order of neighbors is returned by the neighborhood
>   query functions or for Cartesian communicators, it is in
>   the order of the dimensions, in each dimension first the
>   negative and then the positive direction)
>
> Torsten, please return the decision, Variant A or B.
>
> Best regards
> Rolf
>
>
> -- 
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> 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)
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William Gropp
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign