[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Dmitry Karpeev]

On Fri, Feb 10, 2012 at 3:53 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Fri, Feb 10, 2012 at 15:50, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>
>> Why not simply allow DM to return two matrices as SNES and KSP would want
>> anyway?
>
>
> How do you specify the reduced stencil to use for the preconditioning
> matrix? Maybe it wouldn't add too many more if statements to the current
> code which is already polluted with them.
>

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.

Dmitry.
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