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

[Justin Chang]

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!

Justin
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