[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Jed Brown]

On Fri, Feb 10, 2012 at 17:08, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> I think it's completely natural for a DM to assemble two operators -- the
> discretizations for the two are likely to be related anyway -- as soon as
> we decide that it's natural for KSP to take in two matrices and, more
> importantly, for the callback set with DMSetJacobian() to compute two
> matrices: if a DM knows how to compute  two "Jacobians", why wouldn't it
> know how to create/preallocate the two corresponding matrices?


Lots of functions get messy if the DM has multiple ways to do something.
Should DMCreateLocalVector() use the full stencil or the preconditioning
stencil, what should DMGlobalToLocalBegin() be updating, etc.

Barry's solution of having separate DMs sounds cleaner to me, at least
modulo needing conventions about which DM on which to PetscObjectCompose()
things needed by certain callbacks (e.g. in the FAS with TS stuff I'm
doing).
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