On Wed, 17 Sep 2008, Derek Gaston wrote:

> I did look at  Diffsolver... I don't have any problems making them
> match... I just couldn't see how a couple of them mapped.

Ask me any questions you have about the DiffSolver versions; I'll
trust you to figure out what PETSc/Trilinos bits they correspond to.

> The step_tolerance is meant to correspond to something close to your relative 
> step tolerance...

Oh, it's not a linear solve convergence criterion, it's another
nonlinear solve convergence criterion?

> and I would have named it that except I'm not entirely sure that
> Petsc does use a scaled relative step tolerance (as I suspect you
> are doing).  I believe that they use the absolute step size instead
> (which is really a bummer).

DiffSolver does an OR between four tolerances (or whichever you don't
want to ignore by setting to zero), and yes, absolute step size
(absolute_step_tolerance) is one of them, albeit one I rarely use.

>> Of course, the DiffSolver parameters are currently just Reals; we can
>> change those to setter/getter pairs or functions returning references
>> or whatever if you prefer.
>
> This is where I wasn't quite sure what I preferred.  I think functions 
> returning references would be the simplest... that way those functions could 
> be implemented completely in the base NonlinearSolver class.  All 
> Petsc/NoxNonlinearSolver would do is pick up the Reals out of the base before 
> calling solve.
>
> That said... there's not much difference between just exposing Reals and 
> using concrete methods that return references.  So I'm game for either.

Same here; I'll leave it up to you.
---
Roy

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