[petsc-users] Passive DM Variables

Nicholas Arnold-Medabalimi narnoldm at umich.edu
Mon Aug 29 10:24:51 CDT 2022

Yes, this is exactly what I was looking for. Thank you all.

On Mon, Aug 29, 2022 at 8:02 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Sun, Aug 28, 2022 at 12:44 PM Nicholas Arnold-Medabalimi <
> narnoldm at umich.edu> wrote:
>> Hi
>> I'm working on a finite volume implementation using DMPlex. I was
>> wondering what the best-considered way to add cell variables to the DM that
>> we don't want to be part of the ksp/snes solve. As far as I can tell, if I
>> add an extra section with those, they will still be part of the F and U
>> vectors in the solver callbacks (to be expected). But my impression is that
>> that will just inflate the system size even if they have an F=0? Or is the
>> solver able to notice variables that are not dependent for the solve.
>> Alternatively, I have been just making a separate DM with those but that
>> feels a bit clunky especially if any mesh refinement occurs.
> Mark is correct. We have been using a two DM strategy. You can attach this
> auxiliary data using
>   https://petsc.org/main/docs/manualpages/DM/DMSetAuxiliaryVec/
> The idea is that you define a layout for your extra information using a
> new DM, then create a Vec for it, and attach it to the DM. This
> can  be pulled out by any callback function, and the DM can be pulled out
> of the vector. In the Plex pointwise functions for residual
> and Jacobian, auxiliary data is automatically interpolated to the
> quadrature points as well.
> Is this what you were looking for?
>   Thanks,
>      Matt
>> Any advice would be much appreciated.
>> Thanks
>> Nicholas
>> --
>> Nicholas Arnold-Medabalimi
>> Ph.D. Candidate
>> Computational Aeroscience Lab
>> University of Michigan
> --
> 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/>

Nicholas Arnold-Medabalimi

Ph.D. Candidate
Computational Aeroscience Lab
University of Michigan
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