[petsc-users] Shell Matrix Operations required for KSP solvers?

[Dave May]

On Tue, 23 Oct 2018 at 02:24, Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Oct 22, 2018 at 7:44 PM Andrew Ho <andrewh0 at uw.edu> wrote:
>
>> I have a specialized matrix structure I'm trying to take advantage of for
>> solving large scale (non)linear systems. I think for this purpose using a
>> Shell matrix is sufficient for interfacing with PETSc's KSP linear solvers.
>>
>> Looking at the examples which use shell matrices, it seems most only
>> require implementing MatMult, and sometimes MatMultTranspose. Is there a
>> list of what operations are required (or optional but good to have) for the
>> different KSP solver types? This is specifically for the KSP solve itself,
>> not constructing the actual matrix. I'd also be interested if any of the
>> required/optional operations changes if preconditioners (left and/or right)
>> are used.
>>
>
> There is no list, but its hard to think of another operation KSP would ask
> for. Preconditioners are another story unfortunately. They often want
> explicit access to matrix entries. its really unusual for KSPs to work
> without a good preconditioner (the notable exception being well-conditioned
> systems like some boundary integral operators).
>

The most basic PC is Jacobi - for that to work you need to implement
MatGetDiagonal.

Thanks,
  Dave



>   Thanks,
>
>     Matt
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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