[petsc-users] Configure nested PCFIELDSPLIT with general index sets

[Lawrence Mitchell]

> On 21 Mar 2017, at 13:24, Matthew Knepley <knepley at gmail.com> wrote:
> 
> I think the remedy is as easy as specifying a DMShell that has a PetscSection (DMSetDefaultSection) with your ordering, and
> I think this is how Firedrake (http://www.firedrakeproject.org/) does it.

We actually don't use a section, but we do provide DMCreateFieldDecomposition_Shell.

If you have a section that describes all the fields, then I think if the DMShell knows about it, you effectively get the same behaviour as DMPlex (which does the decomposition in the same manner?).

> However, I usually use a DMPlex which knows about my
> mesh, so I am not sure if this strategy has any holes.

I haven't noticed anything yet.

Lawrence