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

[Matthew Knepley]

On Wed, May 17, 2023 at 11:20 AM Berend van Wachem <berend.vanwachem at ovgu.de>
wrote:

> Dear Matt,
>
> Is there a way to 'redo' the DMLocalizeCoordinates() ? Or to undo it?
> Alternatively, can we make the calling of DMLocalizeCoordinates() in the
> DMPlexCreate...() routines optional?
>
> Otherwise, we would have to copy all arrays of coordinates from
> DMGetCoordinatesLocal() and DMGetCellCoordinatesLocal() before
> scaling them.
>

I am likely not being clear. I think all you have to do is the following:

  DMGetCoordinatesLocal(dm, &xl);
  VecScale(xl, scale);
  DMSetCoordinatesLocal(dm, xl);
  DMGetCellCoordinatesLocal(dm, &xl);
  VecScale(xl, scale);
  DMSetCellCoordinatesLocal(dm, xl);

Does this not work?

  Thanks,

     Matt

Best regards, Berend.
>
> On 5/17/23 16:35, Matthew Knepley wrote:
> > On Wed, May 17, 2023 at 10:21 AM Berend van Wachem <
> berend.vanwachem at ovgu.de <mailto:berend.vanwachem at ovgu.de>> wrote:
> >
> >     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?
> >
> >
> > Good question. Right now, the only connection between the two sets of
> coordinates is DMLocalizeCoordinates(). Since sometimes
> > people want to do non-trivial things to
> > coordinates, I prefer not to push in an API for "just" scaling, but I
> could be convinced
> > the other way.
> >
> >    Thanks,
> >
> >       Matt
> >
> >     Thanks, Berend.
> >
> >     On 5/17/23 16:10, Matthew Knepley wrote:
> >      > On Wed, May 17, 2023 at 10:02 AM Berend van Wachem
> >      > <berend.vanwachem at ovgu.de <mailto:berend.vanwachem at ovgu.de>
> <mailto:berend.vanwachem at ovgu.de
> >     <mailto: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/ <
> https://www.cse.buffalo.edu/~knepley/> <
> http://www.cse.buffalo.edu/~knepley/
> >     <http://www.cse.buffalo.edu/~knepley/>>
> >
> >
> >
> > --
> > 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/>
>


-- 
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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