[petsc-users] Initial estimation on SNES and KSP

[Matthew Knepley]

On Thu, Sep 4, 2014 at 12:28 PM, Jed Brown <jed at jedbrown.org> wrote:

> Miguel Angel Salazar de Troya <salazardetroya at gmail.com> writes:
>
> > Dear all
> >
> > SNES uses internally a KSP to solve the linear system of equations right?
> > Now the case that we had a linear system of equations that we are solving
> > with SNES, how could we set the initial estimation for the KSP? If we
> just
> > included the option -ksp_initial_guess_nonzero, the KSP will grab the
> > vector X we passed to the SNES?
>
> You definitely don't want this for Newton-type methods.  If you have a
> nonzero guess for the solution of the linear system, you should have
> evaluated the Jacobian at that point.  A zero initial guess is optimal
> for Newton-type methods.
>

Notice that Newton is solving for the correction, not the solution itself.

  Matt

-- 
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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