[petsc-users] SNES and ghosted vector of unknowns

[Dominik Szczerba]

>> 1) What is 'func' on the SNESSetPicard manual page. It only says
>> "function evaluation routine". What function? Do you mean Ax-b?
>> 2) Is it supposed to perform better / more optimally then using
>> FormFunction with FormJacobian and passing A as the Jacobian?
>
>

What is 'func' on the SNESSetPicard manual page. It only says
"function evaluation routine". What function? Do you mean Ax-b?

> All SNESSetPicard does is evaluate both A and b in "residual evaluation",
> compute F(x) = A(x)x - b(x), and internally cache the matrix A(x). Using it
> is completely optional. If you are willing to write residual evaluation for
> the whole F(x), then you will benefit from having less expensive residual
> evaluations, making line searches and matrix-free Newton (-snes_mf_operator)
> affordable.

I understood from the documentation sec. 5.1 and 5.6 that
-snes_mf_operator is not well suited for unstructured problems, rather
for structured problems with known stencil. Is it not so?

Dominik