[petsc-users] DMSWARM with DMDA and KSP

[Matthew Young]

Thanks for the suggestion to keep DMs separate, and for pointing me toward
that example. I now have a DM for the particle quantities (i.e., density
and flux) and another for the potential. I'm hoping to use
KSPSetComputeOperators with PCGAMG, so I packed the density DM into the
application context and set the potential DM on the KSP, but I'm not sure
how to communicate changes in the KSP DM (e.g., coarsening) to the density
DM inside my operator function.

--Matt
==========================
Matthew Young, PhD (he/him)
Research Scientist II
Space Science Center
University of New Hampshire
Matthew.Young at unh.edu
==========================


On Sun, Apr 30, 2023 at 1:52 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Sun, Apr 30, 2023 at 1:12 PM Matthew Young <
> myoung.space.science at gmail.com> wrote:
>
>> Hi all,
>>
>> I am developing a particle-in-cell code that models ions as particles and
>> electrons as an inertialess fluid. I use a PIC DMSWARM for the ions, which
>> I gather into density and flux before solving a linear system for the
>> electrostatic potential (phi). I currently have one DMDA with 5 degrees of
>> freedom -- one each for density, 3 flux components, and phi.
>>
>> When setting up the linear system to solve for phi, I've been following
>> examples like KSP ex34.c and ex42.c when writing the KSP operator and RHS
>> functions but I'm not sure I have the right approach, since 4 of the DOFs
>> are known and 1 is unknown.
>>
>> I saw this thread
>> <https://lists.mcs.anl.gov/pipermail/petsc-users/2016-November/031031.html>
>> that recommended using DMDAGetReducedDMDA, which I gather has been
>> deprecated in favor of DMDACreateCompatibleDMDA. Is that a good approach
>> for managing a regular grid with known and unknown quantities on each node?
>> Could a composite DM be useful? Has anyone else worked on a problem like
>> this?
>>
>
> I recommend making a different DM for each kind of solve you want.
> DMDACreateCompatibleDMDA() should be the implementation of DMClone(), but
> we have yet to harmonize all things for all DMs. I would create one DM for
> your Vlasov components and one for the Poisson.
> We follow this strategy in our Vlasov-Poisson test for Landau damping:
> https://gitlab.com/petsc/petsc/-/blob/main/src/dm/impls/swarm/tests/ex9.c
>
>   Thanks,
>
>      Matt
>
>
>> --Matt
>> ==========================
>> Matthew Young, PhD (he/him)
>> Research Scientist II
>> Space Science Center
>> University of New Hampshire
>> Matthew.Young at unh.edu
>> ==========================
>>
>
>
> --
> 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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