Using FEInterfaceValues with FESystems?

[blais...@gmail.com]

Dear all,

I hope you are well.

I am currently trying to solve an advection-diffusion equation at very, very high Péclet number. I first implemented a GLS-stabilized continuous Galerkin solution, it works well, but clearly I think a DG approach would be immensely better here.

The issue is that the velocity field for my advection-diffusion stems from a Continuous Galerkin solution with another dof handler, formulated using a FESystem. Everything work well until them. The issue I have is that the FEInterfaceValues does not seem to want to work with FEValuesExtractors? It seems like it cannot use the [] operator to extract my velocity values out of my 4 components (velocity + pressure).

I am sure i'm forgetting something stupid here, but how should I proceed for vector valued problem using DG?

Best

Bruno

[Wolfgang Bangerth]

No, you're not forgetting anything. FEInterfaceValues is still a pretty new
class and nobody has ever written the equivalent of the FEValuesViews classes
that you get from FEValues when you apply an extractor.

I suspect that the effort would not be huge, and that one could just
copy-paste a lot of code from the existing views classes. If you were
interested in doing that, I'd be happy to discuss what I think is going to be
necessary. But the short answer is really that FEInterfaceValues isn't ready
for vector-valued problems at the moment.

Best
Wolfgang

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[blais...@gmail.com]

Good to know.

Let me read the documentation a bit and I  could try to come up with a PR. Maybe this is something we could discuss? I'd be glad to help in improving DG methods :)

[Wolfgang Bangerth]

On 3/11/21 11:10 PM, blais...@gmail.com wrote:
> Let me read the documentation a bit and I  could try to come up with a PR.
> Maybe this is something we could discuss? I'd be glad to help in improving DG
> methods :)

Happy to discuss in whatever venue you propose!

Start by looking at the FEValuesViews::Scalar class. We'd need a corresponding
FEInterfaceValuesViews::Scalar class. Once you know how the former operates,
you will probably be able to see how the latter needs to be implemented. I
foresee a lot of copy-paste of small functions where the only change is in the
2-3 line bodies.

[Timo Heister]

Bruno, I already have a working implementation of the extractors on my
machine. I just didn't get the time to clean up, write tests, and
submit the PR. Sorry. I will try to pick this up again in the next few
days.

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--
Timo Heister
http://www.math.clemson.edu/~heister/

[blais...@gmail.com]

Timo,

Don't worry about that. I can't complain if someone else does the work no? :)