[petsc-users] Jacobian construction, DA vs Plex

[Matthew Knepley]

On Mon, Jul 7, 2014 at 5:36 PM, Tobin Isaac <tisaac at ices.utexas.edu> wrote:

>
> Hi,
>
> If I have a pointwise Jacobian function f, I know that I can call
> DMGetDS() and pass f to PetscDSSetJacobian(), and that f will be used
> by PetscFEIntegrate() and thus by DMPlexSNESComputeJacobianFEM().  It
> looks like PetscFEIntegrate() is only used by plex and not da.  Is
> there anyway that I can use f to construct a Jacobian with a da
> object?
>

There is a completely untested way. My idea is that the DA is able to give
back
cell closures the same way that Plex does, making all the FEM code work just
as it does in the unstructured case. There are a few toy tests of this
functionality
in src/dm/impls/plex/examples/tests/ex3.c. I have not made a thoroughgoing
example which switches between Plex and DA, but it should be possible. Let
me know if it fails.

All this DA code which does not assume a vertex discretization is activated
by
giving it a default section.

  Thanks,

     Matt


>   Toby
>
-- 
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
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