[petsc-users] PetscFE questions

[Matthew Knepley]

On Tue, Oct 18, 2016 at 7:38 AM, Julian Andrej <juan at tf.uni-kiel.de> wrote:

> Hi,
>
> i have general question about PetscFE. When i want to assemble certain
> parts of physics separately, how can i do that? I basically want to
> assemble matrices/vectors from the weak forms on the same DM (and
> avoid copying the DM) and use them afterwards. Is there a convenient
> way for doing that?
>
> The "workflow" i'm approaching is something like:
>
> - Setup the DM
> - Setup discretization (spaces and quadrature) for each weak form i
> want to compute
> - Compute just the weak form i want right now for a specific
> discretization and field.
>
> The reason is i need certain parts of the "complete" Jacobian for
> computations of eigenproblems and like to avoid computing those more
> often than needed.
>

The way I envision this working is to use DMCreateSubDM(). It should extract
everything correctly for the subset of fields you select. However, I have
not
extensively tested, so if something is wrong let me know.

  Thanks,

     Matt


> Regards
> Julian
>



-- 
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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