[petsc-users] KSPBuildSolution

Matthew Knepley knepley at gmail.com
Wed Feb 16 10:05:46 CST 2011

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
to the Newton system is not a descent direction, which is checked by the
line search.


> -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
-- Norbert Wiener
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