[petsc-users] SNES and ghosted vector of unknowns

[Jed Brown]

On Mon, Apr 23, 2012 at 08:11, Dominik Szczerba <dominik at itis.ethz.ch>wrote:

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

Just b(x)


>
> > 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?


You must be thinking of coloring.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120423/32594545/attachment.htm>