[petsc-users] Issues creating DMPlex from higher order mesh generated by gmsh

[Matthew Knepley]

On Mon, May 15, 2023 at 9:30 AM Jed Brown <jed at jedbrown.org> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
>
> > On Fri, May 5, 2023 at 10:55 AM Vilmer Dahlberg via petsc-users <
> > petsc-users at mcs.anl.gov> wrote:
> >
> >> Hi.
> >>
> >>
> >> I'm trying to read a mesh of higher element order, in this example a
> mesh
> >> consisting of 10-node tetrahedral elements, from gmsh, into PETSC. But
> It
> >> looks like the mesh is not properly being loaded and converted into a
> >> DMPlex. gmsh tells me it has generated a mesh with 7087 nodes, but when
> I
> >> view my dm object it tells me it has 1081 0-cells. This is the printout
> I
> >> get
> >>
> >
> > Hi Vilmer,
> >
> > Plex makes a distinction between topological entities, like vertices,
> edges
> > and cells, and the function spaces used to represent fields, like
> velocity
> > or coordinates. When formats use "nodes", they mix the two concepts
> > together.
> >
> > You see that if you add the number of vertices and edges, you get 7087,
> > since for P2 there is a "node" on every edge. Is anything else wrong?
>
> Note that quadratic (and higher order) tets are broken with the Gmsh
> reader. It's been on my todo list for a while.
>
> As an example, this works when using linear elements (the projection makes
> them quadratic and visualization is correct), but is tangled when holes.msh
> is quadratic.
>
> $ $PETSC_ARCH/tests/dm/impls/plex/tutorials/ex1 -dm_plex_filename
> ~/meshes/holes.msh -dm_view cgns:s.cgns -dm_coord_petscspace_degree 2
>

Projection to the continuous space is broken because we do not have the
lexicographic order on simplicies done. Are you sure you are projecting
into the broken space?

  Thanks,

     Matt
-- 
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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20230515/18e9f3be/attachment-0001.html>