[petsc-users] Setting an unknown initial guess

Matthew Knepley knepley at gmail.com
Tue Dec 8 09:30:36 CST 2020

On Tue, Dec 8, 2020 at 8:58 AM David Schneider <dav.schneider at tum.de> wrote:

> Dear all,
> I'm using a KSPLSQR solver without preconditioning and configure the
> solver once in the beginning. Afterwards, I solve my system multiple
> times in a time-dependent system and I would like to use an initial
> guess (from the previous solution). Currently, I use
> `KSPSetInitialGuessNonzero` for this purpose, but it may happen that the
> actual guess is zero. If the initial guess is zero, the solver fails to
> converge, at least with the default configuration. Setting
> `KSPSetInitialGuess` with `PETSC_FALSE` (which should also be the
> default) zeros the guess out. Is there a (native) way to preserve the
> initial guess, but still ensure convergence in the KSPsolver in case the
> guess is zero?

I do not understand. If the solver does not converge for some initial
guess, that
is a function of the solver used. You might need a better preconditioner.



> Thanks in advance,
> David

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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