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

[Berend van Wachem]

Dear Matt,

Thanks for getting back to me so quickly.
If I scale each of the coordinates of the mesh (say, I want to cube each 
co-ordinate), and I do this for both:

DMGetCoordinatesLocal();
DMGetCellCoordinatesLocal();

How do I know I am not cubing one coordinate multiple times?

Thanks, Berend.



On 5/17/23 16:10, Matthew Knepley wrote:
On Wed, May 17, 2023 at 10:02 AM Berend van Wachem 
<berend.vanwac...@ovgu.de <mailto:berend.vanwac...@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/>