[Paraview] Ghost data in parallel formats

[Renato Elias]

> Berk: Do you have the ability to mark a node as "owned" by one partition
and as "ghost" on
> other partitions?

Yes! We classify processes as master and slaves according to their ranking
numbers. After this we can assign the shared node to a master (which will
take care of shared computations) and tell the slave process that this node
is being shared with a master (and the slave process will consider it as a
"ghost" for computations).

The ideas we used in our parallel solver were taken from the following
article:

Karanam, A. K., Jansen, K. E. and Whitinig, C. H., "Geometry Based
Pre-processor for Parallel Fluid Dynamic Simulations Using a Hierarchical
Basis", Engineering with Computers (24):17-26, 2008.

This article was made available from the author in
http://www.scorec.rpi.edu/REPORTS/2007-3.pdf (Figures 7 to 9 explain the
communication method between processes),

Regards

Renato.


On Tue, Mar 1, 2011 at 12:24 PM, Berk Geveci <berk.geveci at kitware.com>wrote:

> Hi Renato,
>
> > I think I'm missing something.... you said cells only?!
> > If I understood this subject correctly, a cell should be considered ghost
> if
> > it's held by more than one partition/process, isn't it?! In this case,
> > there'll be an overlapped layer of elements. The problem is that my MPI
> > solver does not make use of this overlapped layer of cells/elements.
>
> Yep. You understood correctly. Ghost cells are very common for finite
> difference calculations but not as common for finite elements.
>
> > It only
> > has nodes/points that are shared by processes. This explains why I asked
> by
> > a ghost node (shared node would be more appropriated to define such kind
> of
> > node).
> > Can I consider a cell as ghost if it touches the parallel interface
> (without
> > overlapping)? Would it work?
>
> Nope. Then you'd start seeing gaps. The right thing to do is for
> ParaView to support ghost points (nodes) better. However, this is
> non-trivial in some cases. For removing internal interfaces, it is
> sufficient to mark points as ghosts. However, for accurately
> performing statistics, you need to make sure that you count all points
> only once, which requires assigning ghost nodes to processes. So a
> replicated node would be marked as ghost (a better word is shared) and
> also owned by a particular process. We are going to improve VTK's
> ghost level support. This is something we'll support. However, it will
> be up to the simulation to produce the write output. Do you have the
> ability to mark a node as "owned" by one partition and as "ghost" on
> other partitions?
>
> Best,
> -berk
>



-- 
Renato N. Elias
=============================================
Professor at Technology and Multilanguage Department (DTL)
Federal Rural University of Rio de Janeiro (UFRRJ)
Nova Iguaçu, RJ - Brazil

=============================================
Researcher at High Performance Computing Center (NACAD)
Federal University of Rio de Janeiro (UFRJ)
Rio de Janeiro, Brazil
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