[petsc-dev] attaching field information to PetscLayout?

[Jed Brown]

On Sun, May 15, 2011 at 05:33, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> Would it be dangerous to be adding fields to a PetscLayout shared by
> many Vecs/Mats (hence, PCs)?
>

I think PetscLayout should be strictly immutable after PetscLayoutSetUp().

Yes, in fact, a field, at least in my mind, is more than just
> combinatorial information (IS), and might
> involve some linear-algebraic information (e.g., if getting the
> corresponding subvec or updating
> the containing vec requires a linear transformation).
>

I think this might be snowballing beyond what is reasonable to handle at
this level. Someone might say that converting [Density,Momentum,Energy] to
[Pressure,Velocity,Temperature] has some semantic meaning to them and they
want to tell PETSc about it, but it may be a hard sell to demonstrate that
an equation of state belongs in PetscLayout. This example isn't even
contrived though: the relevant Schur complement for preconditioning low-Mach
Euler is a parabolic operator in the pressure space, despite the fact that
pressure is not a conserved variable (thus not explicitly present in the
original system).
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