[petsc-dev] resurrecting the finite element energy functions thread

[Matthew Knepley]

On Wed, Jan 22, 2014 at 4:16 PM, Geoffrey Irving <irving at naml.us> wrote:

> On Tue, Jan 21, 2014 at 9:52 PM, Jed Brown <jed at jedbrown.org> wrote:
> > Lisandro Dalcin <dalcinl at gmail.com> writes:
> >> I thought to do that in PetIGA, but then realized that a reducer+eval
> >> at quadrature points+MPI_MAX sounds weird (though I can imagine some
> >> use cases). A reduce with MPI_MAX is a lucky consequence of computing
> >> integrals through quadrature.
> >
> > Suppose we want to know the max stress in a structure to determine
> > whether it will be damaged by a given loading scenario?  The quadrature
> > points are not sufficient to determine a max stress for the discrete
> > solution, but it is a convergent method for determining the max stress
> > of the continuum structure.
>
> So I wrote PetscFEIntegrateScalars, but then realized that I have no
> idea how to organize the DM level.  Residuals and jacobians can be
> only be "turned on" via DMSNESSetFunctionLocal, and then accessed via
> the SNES.  This would work in the specific case of an objective, but
> not for the general case where we're integrating some arbitrary number
> of PetscScalars.
>
> Where should the outer "integrate a bunch of scalars over a DM with a
> bunch of PetscFE" objects go, and what should it be called?  The
> naming conventions at this level are rather obscure.
>
> Relatedly, is it going to be a problem if I want to use PetscFE
> routines outside an SNES, such as inside a TAO optimization problem?
> Should I make a dummy SNES and then point TAO to SNESComputeObjective
> and such, or is there a cleaner way?


1) I have been putting functions like this (DMPlexComputeL2Diff) in DM
because there
seemed to be no other place.

2) Nope you can use them anywhere

  Matt


> 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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