[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Jed Brown]

On Thu, Feb 9, 2012 at 23:41, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> Currently DMGetMatrix(DM dm, MatType mattype , Mat *J)  is supposed to
> produce the system Jacobian, according to the docs.
> SNES will use it, but, since DMGetMatrix returns a single matrix, it can't
> use a different preconditioning matrix.
> Why not change this to DMGetMatrices(DM dm, MatType jtype, Mat *J, MatType
>  ptype, Mat *P)?
> I'm not exactly sure what the best way of handling MatType should be (same
> MatType for J and P, separate types, how dm->mattype
> affects the result), but I think it can be sorted out, whereas the absence
> of P is a clear limitation.
>

Umm, this doesn't put in values, it just creates a matrix of the right
size. You can make two if you want two different matrices.

If you are talking about DMDAFormJacobianLocal(), that does actually
restrict what you can do, and you have to hack it a bit to use two
different matrices (except by MFFD because the library specifically
supports that).
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