[petsc-dev] Separate operators for jacobian and preconditioner matrix on coarse MG levels

[Lawrence Mitchell]

On 24 Feb 2015, at 19:27, Matthew Knepley <knepley at gmail.com> wrote:

> That is what happens. It does check for snes->jacobian, but that would not
> be
> set on coarse levels anyway. I think we should have an option that makes
> SNESSetUpMatrices() create two matrices.

In the general case, snes->jacobian and snes->jacobian_pre will have different sparsity, but if I just call back to DMCreateMatrix twice I won't know which one to make.  One way to fix this would be for DMCreateMatrix to have the option of creating two matrices at once:

DMCreateMatrix(dm, Mat *mat, Mat *pmat)

One could then call

DMSetCreateMatricesSeparately(PETSC_TRUE)

(better names much appreciated).

to indicate that one wants separate matrices for the jacobian and its pmat.

Thoughts?

Lawrence
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