[petsc-dev] coordinates stored twice in snes ex12?

Matthew Knepley knepley at gmail.com
Tue Nov 19 15:23:09 CST 2013

On Tue, Nov 19, 2013 at 3:19 PM, Geoffrey Irving <irving at naml.us> wrote:

> On Tue, Nov 19, 2013 at 1:14 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
> > On Tue, Nov 19, 2013 at 1:14 PM, Geoffrey Irving <irving at naml.us> wrote:
> >>
> >> It looks like when ex12 clones the DM, it reuses the mesh data
> >> structure but copies the coordinate vector.  Is there a reason it
> >> can't reuse that storage?  Given that the PetscFEM routines accept the
> >> same position array for dependent and auxiliary fields, does it even
> >> make sense to have distinct coordinate arrays?
> >
> >
> > Yes, this is lazy. It could be replaced by
> >
> > DMGetCoordinateSection(dm, &s)
> > DMGetCoordinatesLocal(dm, &c)
> > DMSetCoordinateSection(dmAux, s)
> > DMSetCoordinatesLocal(dmAux, c)
> Does it matter that dm's section knows about boundary conditions, and
> dmAux's currently doesn't?  This change would mean that both sections
> know about boundary conditions.

The coordinate section is a different thing which describes coordinate
There are no BC in the coordinate sections, only in the default sections.
aux has a different default section for the layout of the coefficient.

> Should I make this change to ex12 and remove the SetupMaterialSection
> function entirely, or should I only use it in my own code?

We still need SetupMaterialSection() if we are running with a material


> Thanks,
> Geoffrey

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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