[petsc-dev] Reading periodic meshes from GMSH

[Matthew Knepley]

On Thu, Jul 12, 2018 at 10:00 AM Lawrence Mitchell <
lawrence.mitchell at imperial.ac.uk> wrote:

>
> > On 12 Jul 2018, at 12:27, Stefano Zampini <stefano.zampini at gmail.com>
> wrote:
> >
> > Lawrence,
> >
> > I wrote the periodic GMSH reader and I can answer for it.
> >
> > With DMPlex, when we have periodicity, we currently have two ways of
> encoding it
> >
> > 1) through the maxCell concept (or, as Lisandro's like to call it, the
> "maxCell crap")
> > 2) through the coordinatesSection
> >
> > Since periodicity with general meshed cannot be encoded with 1), I
> populate the cell part of the coordinates section with the "localized
> coordinates" (only for periodic cells), and leave all the other dofs
> associated with the vertices.
> > I believe this kind of localization is also what you get with the
> maxCell crap (check it out with the BoxMesh): even in this case in the
> coordinate section you have cell dofs only for cells touching the periodic
> boundary, and all the vertices have their own coordinates.
> > Look eg in DMPlexComputeLineGeometry_Internal.
> >
> > What you know for sure is that the first 6 entries of the closure are
> the ones you should look for (not the size of the closure)
>
> Thanks.  This seems somewhat odd to me.  At the periodic boundary, the
> coordinate field is not single-valued, so I don't understand how you can
> reasonably put coordinate dofs on the vertices.  I would have thought that
> on the periodic cells, the vertices in the closure have no dofs in the
> coordinate section, and it's just the cell that has dofs associated with it.
>
> Is there a reason why you leave things on the vertices at all?
>

You can think of it being multi-values, or you can think of the vertex
values as lying on a specific Riemann sheet.

   Matt


> Cheers,
>
> Lawrence



-- 
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.caam.rice.edu/~mk51/>
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