[petsc-users] Create a DM given sets of IS's

[Matthew Knepley]

On Mon, Dec 31, 2018 at 2:40 AM Justin Chang via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Hi all,
>
> I am solving a six field battery problem (concentration and potential for
> each of the two solid and one electrolyte domains) and I want to experiment
> with nested/recursice fieldsplitting. I have the IS's and am able to use
> these to define my PCFieldSplitsSetIS(). However, I can imagine this
> getting really messy from a programming standpoint, especially once I need
> to add temperature into the mix, so it is my hope that I can translate
> these index sets and fields into a DM (maybe DMShell?) so that I can just
> rely on command line options to play around with various combinations of
> field assignments and splits (e.g. -pc_fieldsplit_X_fields)
>
> However, it doesn't seem clear to me how I would create a DM when you
> already know the IS's for each fields. If I understand functions like
> DMCreateFieldDecomposition() correctly, it seems that it returns to you the
> IS's and sub DM's associated with the original DM, whereas I want to do it
> the other way around. Perhaps the "reversal" of something like
> DMCreateFieldIS()
> <https://www.mcs.anl.gov/petsc/petsc-dev/src/dm/interface/dm.c.html#DMCreateFieldIS>,
> where you convert the IS into a PetscSection or is there an easier/better
> way?
>
> Any thoughts/help appreciated!
>

Paul has recently done this for LibMesh. I believe that constructing a
PetscSection is enough to get you minimally started. That allows
DMCreateSubDM() to work by subsetting the Section, and that should allow
the command line to work. CreateFieldDecomposition() should
be removed I think.

  Thanks,

    Matt


> Justin
>


-- 
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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