[petsc-users] preconditioner for -snes_fd or -snes_fd_color

[Peter Brune]

On Fri, Apr 4, 2014 at 3:57 PM, Xiangdong <epscodes at gmail.com> wrote:

> Hello everyone,
>
> If we use -snes_fd or -snes_fd_color, can we still pass a preconditioner
> to snes/ksp?
>
> In snes/ex1.c, when I use -snes_fd, the program never calls the
> FormJacobian1 to get the preconditioner.
>

FormJacobian1 forms... wait for it... the Jacobian!  Not the
preconditioner.  -snes_fd and -snes_fd_color replace the Jacobian-forming
routine.


>
> Any suggestions about providing preconditioner to snes_fd or snes_fd_color?
>
>
Both of these explicitly create the approximate Jacobian matrix by using
finite differences, so they may be used with any preconditioner.  -snes_mf
is a different beast entirely and merely approximates the action of the
matrix without forming it, which is where the preconditioner issues come in.

- Peter


> Thanks.
>
> Xiangdong
>
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