[petsc-dev] KSP rtol

Jed Brown jedbrown at mcs.anl.gov
Wed Dec 14 21:29:18 CST 2011

On Wed, Dec 14, 2011 at 13:50, Mark F. Adams <mark.adams at columbia.edu>wrote:

> What I am doing is classic inexact Newton (or it looks like these folks
> are doing Picard).

It appears that they are doing Picard in one-shot mode instead of in defect
correction mode. If you write it as a defect correction, then the initial
guess will be zero and the standard tolerance is the correct one. I
maintain that defect correction is better in every way for solvers, and it
naturally gives you a nonlinear residual so that you can use a reliable
nonlinear solver tolerance.
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