[petsc-dev] SNES, Coloring, DM, and TS

[Jed Brown]

On Mon, Feb 27, 2012 at 11:00, Matthew Knepley <knepley at gmail.com> wrote:

> I don't see why this is a dependency loop.
>

1. The callback interface is duplicated.

2. DM callbacks should provide a way for the called code to get access to
the TS or DM so that users aren't prevented from doing hacky things.


>
>
>> As a related matter, I'm stuck with a reference counting loop where I
>> want to attach special Vecs to a DM. I can wrap them in a PetscContainer to
>> circumvent the code that checks for reference cycles, but that makes
>> freeing them delicate. We could make a named cache similar to DM work
>> vectors, but where restored Vecs are not available for reuse.
>>
>
> I know that rationale for having Vecs know about a DM (output), which I
> don't like. What is the rationale for having DMs know about a certain Vec?


A TS wants to solve a nonlinear problem using FAS, so it needs to implement
a callback on levels. So it coarsens the grid, but it also needs to coarsen
the affine vectors so that it can define the finite-step problem on coarse
levels.

Same issue for lots of cases where a user needs to save grid setup,
coefficient fields, etc on levels so that it is available in a callback.
It's natural to compose those vectors with the DM, but that creates a
reference loop.
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