[petsc-users] Does PetscFE framework allow use of Hdiv and Hcurl elements ?

[Matthew Knepley]

On Tue, Sep 4, 2018 at 7:34 PM Rochan Upadhyay <u.rochan at gmail.com> wrote:

> Dear Petsc Users and Developers,
>
> Upon looking at the function listings and their descriptions in the manual
> suggests that the only finite element that can be automatically used is the
> continuous Lagrange. Is it possible to "easily" use vector valued Hcurl and
> Hdiv elements (like RT, NED, BDM and other more exotic types) ?
>

The short answer is no.


> It seems that there are two methods for generating finite elements : (1)
> Compute nodal basis functions from orthogonal polynomials with DOFs defined
> as pointwise evaluations (PETSCSPACEPOLYNOMIAL) (2) Compute basis functions
> at quadrature points yourself and input them directly (PETSCSPACEPOINT).
> Even if you input the trial and test basis functions this way, how would we
> input the various types of Piola transforms needed to map real to reference
> space. It seems in the implementation at "EvaluateFieldJets" only the
> covariant Piola transform (using invJ) is hard coded.
>

True. Toby has a branch that fixes this and will support Hdiv and Hcurl.
However, I do not know how many weeks away we
are on this project since the semester has now started.


> Also I cannot find a good documentation of Petsc FE capabilities (unlike
> the superb presentations describing the DM routines).
>

Yes, this is somewhat on purpose. PetscFE/FV exist principally to generate
examples for me, and to help us
understand how discretizations should interact with meshes and solvers. We
have not yet decided whether
PETSc will officially support discretizations, or just use something like
Firedrake or Libmesh. However, I think
pushing on this has made those packages better, so its not a waste of time.

So, I am willing to explain anything you want on the list, and try and
translate those explanations to documentation.
Also, we accept documentation Pull Requests (even a few words long), and
Patrick Sanan did a nice presentation
at PETSc 2018 on how to easily submit them through the web interface. I
have since tried it and its easy.

  Thanks,

     Matt


> For me, it is preferable to use Petsc directly for FEM as other packages
> like fenics, libmesh etc.are too bulky, require too much effort to learn
> and not so easy to experiment with.
>
> Regards,
> Rochan
>


-- 
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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