Trust Region problem

Matthew Knepley knepley at
Sat Mar 17 08:15:41 CDT 2007

On 3/17/07, Gong Ding <gdiso at> wrote:
> Hi all,
>    I use PETSC's nonelinear solver to do
> emiconductor simulation. I found a strange problem
> with trust region solvers. It usually works well
> if LU method is used for inner linear solver. But
> when krylov method i.e. GMRES, is employed, it
> often stops due to pnorm is small, but still
> remains large error of function norm. How to solve
> this problem? LU method is much slower than i.e.

This sounds like GMRES is not actually converging (you can check this
using -ksp_monitor). You need a more powerful preconditioner, which
unfortunately usually depends a lot on the problem.


> G.D.
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