[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Matthew Knepley]

On Fri, Feb 10, 2012 at 3:58 PM, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

>
>
> 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.
>

This makes no sense to me unless the two matrices being returned have
different sparsity patterns, and we have no
good way for specifying that, or even a good rationale for doing it.

   Matt


> Dmitry.
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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