[petsc-users] DMPlex - Section.

[Matthew Knepley]

On Thu, Mar 31, 2016 at 10:56 AM, Afanasiev Michael <
michael.afanasiev at erdw.ethz.ch> wrote:

> Hi,
>
> I’d like to define vectors on a subset of points defined by a DM (created
> by DMPlex). For example, if I’m modelling wave propagation in a model with
> both solid and fluid regions, I’d like to define ux, uy, uz vectors in the
> solid part, and p in the acoustic part. Basically, just a varying number of
> dofs per integration point. Looking through the documentation I’ve found a
> pretty comprehensive discussion of setting up the PetscSection object. Is
> an inroad here to define a custom PetscSection on a subset of elements,
> faces, edges, vertices, etc….? Or is there a better way to approach this
> problem? Or is this functionality supported at all? We’re pretty familiar
> with PLEX by now, just looking for ways to define vectors on subsets of the
> whole domain.
>

You can certainly have 0 dofs on any mesh point, so defining a vector on
part of the domain is easy.
This is enough for your case I think.

If you wanted to do this for many very small pieces, then in order for
PetscSection to be efficient, you
would have to consecutively number the points on those pieces, which seems
too hard. For this case,
I would make separate subDMs.

  Matt


> Thanks,
> Mike.
> --
> Michael Afanasiev
> Ph.D. Candidate
> Computational Seismology
> Institut für Geophysik
> ETH Zürich
>
> Sonneggstrasse 5, NO H 39.2
> CH 8092 Zürich
> michael.afanasiev at erdw.ethz.ch
>
>


-- 
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
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