[petsc-users] KSPBuildSolution

[Matthew Knepley]

On Wed, Feb 16, 2011 at 10:04 AM, Juha Jäykkä <juhaj at iki.fi> wrote:

> Since I got two emails before I could reply to one, I am replying to both
> simultaneously.
>
> > It is a good idea to use -ksp_type preonly -pc_type lu to start until you
> > understand the problem.
>
> Matthew: Thanks, but I still get diverging line searches.
>
> > Your Jacobian may be incorrect, try running with -snes_mf_operator
> -pc_type
> > lu -ksp_monitor. The linear solves should converge in 1 iteration. You
> can
> > also try -mat_mffd_type ds if the residual is ill-conditioned.
>
> Jed: I am running with a FD Jacobian just to make sure my hand-written one
> is
> not the culprit. Is there any reason to suspect this might be the reason?
>

Yes, line search failure often occurs for incorrect Jacobians because the
solution
to the Newton system is not a descent direction, which is checked by the
line search.

   Matt


> -Juha
>
> --
>                 -----------------------------------------------
>                | Juha Jäykkä, juhaj at iki.fi                     |
>                | http://www.maths.leeds.ac.uk/~juhaj           |
>                 -----------------------------------------------
>



-- 
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
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