[petsc-users] DMPlex with spring elements

[Matthew Knepley]

On Thu, Sep 25, 2014 at 5:15 PM, Miguel Angel Salazar de Troya <
salazardetroya at gmail.com> wrote:

> > If you need a symmetric Jacobian, you can use the BC facility in
> > PetscSection, which eliminates the
> > variables completely. This is how the FEM examples, like ex12, work.
>
> Would that be with PetscSectionSetConstraintDof ? For that I will need the
> PetscSection, DofSection, within DMNetwork, how can I obtain it? I could
> cast it to DM_Network from the dm, networkdm,  declared in the main
> program, maybe something like this:
>
> DM_Network     *network = (DM_Network*) networkdm->data;
>
> Then I would loop over the vertices and call PetscSectionSetConstraintDof if it's a boundary node (by checking the corresponding component)
>
> I admit to not completely understanding DMNetwork. However, it eventually
builds a PetscSection for data layout, which
you could get from DMGetDefaultSection(). The right thing to do is find
where it builds the Section, and put in your BC
there, but that sounds like it would entail coding.

  Thanks,

     Matt


> Thanks for your responses.
>
> Miguel
>
>
>
> On Thu, Sep 25, 2014 at 2:42 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> Matthew Knepley <knepley at gmail.com> writes:
>>
>> > On Thu, Sep 25, 2014 at 1:46 PM, Abhyankar, Shrirang G. <
>> abhyshr at mcs.anl.gov
>> >> wrote:
>> >
>> >> You are right. The Jacobian for the power grid application is indeed
>> >> non-symmetric. Is that a problem for your application?
>> >>
>> >
>> > If you need a symmetric Jacobian, you can use the BC facility in
>> > PetscSection, which eliminates the
>> > variables completely. This is how the FEM examples, like ex12, work.
>>
>> You can also use MatZeroRowsColumns() or do the equivalent
>> transformation during assembly (my preference).
>>
>
>
>
> --
> *Miguel Angel Salazar de Troya*
> Graduate Research Assistant
> Department of Mechanical Science and Engineering
> University of Illinois at Urbana-Champaign
> (217) 550-2360
> salaza11 at illinois.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
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