dolfin team mailing list archive

[Shawn Walker <walker@xxxxxxxxxxxxxxx>]

I may be missing part of the argument here, but for the case when a user 
defined function is something like exp(x^2 + y^2), could we just pass a 
function pointer (for this particular function) to the interpolation 
routine?  In MATLAB, this type of thing is easy because of function 
handles.  I know we don't have that luxury, but a function pointer kind of 
does this.

Sorry, if I am not understanding the issue.

- Shawn

On Tue, 21 Oct 2008, Garth N. Wells wrote:

> Anders Logg wrote:
> > On Tue, Oct 21, 2008 at 04:45:01PM +0100, Garth N. Wells wrote:
> > > I have a few questions and thoughts regarding the new Function design
> > >
> > > * It's not clear to me what the intention is with user-defined
> > > functions. The functions Function::interpolate(...) never call eval(..),
> > > so they can't pick up user-defined values. Should Function::interpolate
> > > test for the presence of a GenericVector to decide whether or not the
> > > Function is discrete or user-defined?
> >
> > Yes, sorry. I've missed this. I'll fix it.
> >
> > > * It would be useful to declare user-defined functions without
> > > associating a FunctionSpace. If we want to interpolate the function, a
> > > FunctionSpace must then be provided. Anyone see any problems with this?
> >
> > The reasoning here is that all Functions must always be associated
> > with a FunctionSpace so that they may be correctly interpreted in
> > forms and correctly plotted. When a Function is created in PyDOLFIN,
> > it must always be associated with a certain FiniteElement (and in a
> > while FunctionSpace). It would simplify the handling of Functions if
> > they are always associated with a FunctionSpace.
>
> I agree that is makes life simple if every function has a space, but it
> is a bit clunky for declaring user-defined functions. The forms must be
> declared first to extract the finite element to create the function
> space. Could look nasty when a lot of functions are involved.
>
> We have a function Function::interpolate which takes a function space V
> as an argument and it interpolates the function u in V. What if we
> permit undefined function spaces (which perhaps only have a domain)? We
> would then interpolate the user defined function u in the provided space V.
>
> Garth
>
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