[petsc-users] DMPlex: Mapping cells before and after partitioning

[Matthew Knepley]

On Thu, Jan 9, 2020 at 1:35 PM 'Bisht, Gautam' via tdycores-dev <
tdycores-dev at googlegroups.com> wrote:

>
> > On Jan 9, 2020, at 2:58 PM, Jed Brown <jed at jedbrown.org> wrote:
> >
> > "'Bisht, Gautam' via tdycores-dev" <tdycores-dev at googlegroups.com>
> writes:
> >
> >>> Do you need to rely on the element number, or would coordinates (of a
> >>> centroid?) be sufficient for your purposes?
> >>
> >> I do need to rely on the element number.  In my case, I have a mapping
> file that remaps data from one grid onto another grid. Though I’m currently
> creating a hexahedron mesh, in the future I would be reading in an
> unstructured grid from a file for which I cannot rely on coordinates.
> >
> > How does the mapping file work and how is it generated?
>
> In CESM/E3SM, the mapping file is used to map fluxes or states between
> grids of two components (e.g. land & atmosphere). The mapping method can be
> conservative, nearest neighbor, bilinear, etc. While CESM/E3SM uses
> ESMF_RegridWeightGen to generate the mapping file, I’m using by own MATLAB
> script to create the mapping file.
>
> I’m surprised that this is not an issue for other codes that are using
> DMPlex. E.g In PFLOTRAN, when a user creates a custom unstructured grid,
> they can specify material property for each grid cell. So, there should be
> a way to create a vectorscatter that will scatter material property read in
> the “application”-order (i.e. order before calling DMPlexDistribute() ) to
> ghosted-order (i.e. order after calling DMPlexDistribute()).
>

We did build something specific for this because some people wanted it. I
wish I could purge this from all simulations. Its
definitely destructive, but this is the way the world currently is.

You want this:


https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMPLEX/DMPlexNaturalToGlobalBegin.html

    Thanks,

     Matt


> > We can locate points and create interpolation with unstructured grids.
> >
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-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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