dolfin team mailing list archive

[Jed Brown <jed@xxxxxxxx>]

On Tue 2008-11-11 13:05, mspieg wrote:
> On a related thread,
>    I think there is a bug in the Newton solvers (in 0.8.1) in that they now
> don't   zero the correction dx before each linear solve.  For direct solvers
> this isn't a problem, however for krylov methods (in particular
> PETScKrylovSolver), this ends up passing the last correction as the initial
> guess for the next iteration.  Eventually, when the residual becomes
> sufficiently small, this throws a divergence_tolerance error in Petsc. (To see
> this, just change the solver in demo/nls/nonlinearpoisson to something like
> gmres/ilu and use Petsc as the back end).

This is absolutely correct.  I didn't understand Garth's comment earlier
in this thread

> > It's also useful for Newton solvers.

How would you obtain a guess of the next Newton correction?

Jed

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