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

[Lawrence Mitchell]

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Hi all,

I'd like to be able to provide a matrix that is different to the
actual operator for preconditioning purposes on coarse levels.  I
think I see how to do this for PCMG, I do KSPSetComputeOperators which
migrates to the DM and will be called to setup the operators on first
KSPSolve calls.

On the other hand, for FAS, it looks like there is no way to do this:

The SNESen on each level will call SNESSetupMatrices which, if the
snes doesn't have a jacobian matrix set, will call DMCreateMatrix once
to create snes->jacobian and use that for both the jacobian and the
preconditioner for the jacobian.  Is this right, or do I have the
wrong end of the stick?

Cheers,

Lawrence
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