[petsc-users] DMSWARM with DMDA and KSP

[Matthew Knepley]

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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