[petsc-users] Quasi newton

Matthew Knepley knepley at gmail.com
Tue May 3 05:51:18 CDT 2022

On Tue, May 3, 2022 at 2:58 AM Pierre Seize <pierre.seize at onera.fr> wrote:

> Hi,
> If I may, is this what you want ?
> https://petsc.org/main/docs/manualpages/SNES/SNESSetLagJacobian.html

Yes, this is a good suggestion.

Also, you could implement an approximation to the Jacobian.

You could then improve it at each iteration using a secant update. This is
what the Generalized Broyden methods do. We call them NGMRES.



> Pierre
> On 03/05/2022 06:21, Tang, Qi wrote:
> > Hi,
> > Our code uses FDcoloring to compute Jacobian. The log file indicates
> most of time is spent in evaluating residual (2600 times in one Newton
> solve) while it only needs 3 nonlinear iterations and 6 total linear
> iterations thanks to the fieldsplit pc.
> >
> > As a temporary solution, is it possible to evaluate Jacobian only once
> in one Newton solve? This should work well based on my other experience if
> pc is very efficient. But I cannot find such a flag.
> >
> > Is there any other solution, other than implementing the analytical
> Jacobian?
> >
> > Thanks,
> > Qi

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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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