[dune-pdelab] DiscreteGridFunction interface

[Jö Fahlke]

Am Wed,  8. Aug 2012, 15:57:34 +0200 schrieb Christian Engwer:
> On Wed, Aug 08, 2012 at 03:15:29PM +0200, Jö Fahlke wrote:
> > Am Wed,  8. Aug 2012, 10:10:53 +0200 schrieb Christian Engwer:
> > > I'd like to get a new topic on the never ending
> > > interface-discussion-list.
> > > 
> > > Why doesn't the DiscreteGridFunction allow the evaluation of
> > > derivatives? 
> > > 
> > > DiscreteGridFunction is based on the LocalFunctions which allow to
> > > evaluate derivatives and tell till which order. If nobody comes up
> > > with a good reason not to do it, I'd like to include such
> > > functionality in the DiscreteGridFunction. I currently have the
> > > problem, that I'd like to implement different kinds of error
> > > functionals, some of them work require the gradient, some the function
> > > itself and I would prefer not to expose this part to the user.
> > 
> > One reason is that the GridFunction interface does not include evaluating the
> > derivatives.
> 
> Well, this is not really a reason. The interface in some sense is also
> a description of what is there.
> 
> > Another reason is that the local-valued LocalFiniteElements only provide
> > local-valued derivatives.  You still need to know which transformation to
> > apply, which (in general) depends on the kind of element.  This is of course a
> > non-issue with global-valued finite elements.
> 
> Again it is not _really_ a reason. It is just that it is somewhat
> harder to do it, but doesn't really give a reason why not to do it now.

Rereading your question again I see I gave answers to a slightly different
question.  All the reasons mentioned were reasons why nobody had done this up
to now.  They're definitely not hard reasons why this shouldn't be done.

As I said, I think it's a good idea to do let the GridFunction provide the
derivates, where available.

Regards,
Jö.

-- 
Jorrit (Jö) Fahlke, Interdisciplinary Center for Scientific Computing,
Heidelberg University, Im Neuenheimer Feld 368, D-69120 Heidelberg
Tel: +49 6221 54 8890 Fax: +49 6221 54 8884

Kiss a non-smoker; taste the difference.
-- fortune
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