[petsc-dev] getting data out of a PetscFE simulation

[Geoffrey Irving]

On Wed, Jan 29, 2014 at 11:36 AM, Jed Brown <jed at jedbrown.org> wrote:
> Matt's sample code doesn't set it either. We need to fix (and the *only* acceptable fix if that VecView always does the right thing, because we have to be able to call it in analysis settings that know nothing about your discretization).

Matt's sample code doesn't set it either, but for Matt's sample code I
know where to insert the one line call to DMPlexProjectFunctionLocal.
For your version I never have explicit access to the local vector, so
I can't insert the fix.

> The problem is that some vectors reside in a homogeneous space (e.g. increments and eigenvectors) while others reside in the inhomogeneous space (solutions). We can add a flag or BC attribute on the vector to this effect, but this (and slip conditions) was the issue that led me to conclude that removing boundary nodes was mostly a false economy.

To leave the boundary conditions in, we would need efficient support
for a very large, very sparse MatNullSpace.  This is doable via
shells, but is it easy to do in a way that doesn't interfere with the
user's other null spaces?

Geoffrey