itaps-parallel Neighbor definition

[Tim Tautges]

I forgot to mention that this definition is tentative and subject to 
approval from the small subgroup (Onkhar, Carl, Mark M.) discussing the 
issue after Lori left the telecon.

- tim

Tim Tautges wrote:
> A question arose in yesterday's telecon on what constitutes a part 
> neighbor.  After some discussion, we came up with the following 
> definition and rationale.
> 
> Def: for a given part, a part neighbor of dimension d is any other part 
> which shares mesh entities of dimension d with that part (i.e. the 
> entity is represented on both parts).
> 
> Rationale:
> - it is desirable to tie the definition of a part neighbor with 
> information intrinsic to the mesh, i.e. one could derive information 
> about part neighbors using only information about the mesh entities and 
> the partition of entities over processors
> 
> - in general, applications will have other criteria determining which 
> other processors a given processor communicates with; that information 
> can be stored in iMesh using sets and tags already, and applications 
> will presumably be able to pass those things to communication functions 
> in the itaps parallel interface (thus driving the application-specific 
> communication patterns)
> 
> Question: are ghosted/copied entities between parts considered shared? I 
> would assert that ghosting/copying should be between processors, not 
> parts, so this question is not relevant with respect to part neighbors.
> 
> - tim
> 

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              Tim Tautges            Argonne National Laboratory
          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
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