[petsc-users] DMGetCoordinatesLocal and DMPlexGetCellCoordinates in PETSc > 3.18

[Matthew Knepley]

On Wed, May 17, 2023 at 10:02 AM Berend van Wachem <berend.vanwachem at ovgu.de>
wrote:

> Dear PETSc Team,
>
> We are using DMPlex, and we create a mesh using
>
> DMPlexCreateBoxMesh (.... );
>
> and get a uniform mesh. The mesh is periodic.
>
> We typically want to "scale" the coordinates (vertices) of the mesh, and
> to achieve this, we call
>
> DMGetCoordinatesLocal(dm, &coordinates);
>
> and scale the entries in the Vector coordinates appropriately.
>
> and then
>
> DMSetCoordinatesLocal(dm, coordinates);
>
>
> After this, we localise the coordinates by calling
>
> DMLocalizeCoordinates(dm);
>
> This worked fine up to PETSc 3.18, but with versions after this, the
> coordinates we get from the call
>
> DMPlexGetCellCoordinates(dm, CellID, &isDG, &CoordSize,
> &ArrayCoordinates, &Coordinates);
>
> are no longer correct if the mesh is periodic. A number of the
> coordinates returned from calling DMPlexGetCellCoordinates are wrong.
>
> I think, this is because DMLocalizeCoordinates is now automatically
> called within the routine DMPlexCreateBoxMesh.
>
> So, my question is: How should we scale the coordinates from a periodic
> DMPlex mesh so that they are reflected correctly when calling both
> DMGetCoordinatesLocal and DMPlexGetCellCoordinates, with PETSc versions
>  >= 3.18?
>

I think we might have to add an API function. For now, when you scale the
coordinates,
can you scale both copies?

  DMGetCoordinatesLocal()
  DMGetCellCoordinatesLocal();

and then set them back.

  Thanks,

     Matt


> Many thanks, Berend.

-- 
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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