[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Jed Brown]

On Fri, Feb 10, 2012 at 15:58, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> It seems to me that the sparsity pattern (and even the type of the
> matrices) is up to the particular DM type,
> so it is, in principle, opaque.  DMDA can control it by manipulating
> stencil width or widths, while FEM-oriented DM
> types (e.g., libMesh) could control it via the element type, etc. The
> generic DM interface doesn't have a way to specify
> the sparsity pattern. As it should be, in my opinion.
>

Yes, it's fine for DM to have a way to allocate a sparser preconditioning
matrix. The most common case in practice is MFFD for the true Jacobian and
more compact stencil for the preconditioner. It just makes the interface
and implementation a bit ugly/confusing to support both. It would be nice
to have a more elegant way to state it.
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