dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/10/21 Garth N. Wells <gnw20@xxxxxxxxx>:
>
>
> 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.
>>
>>
>
> Something else to think about is that user-defined functions don't have
> a dof map, so we need can't initialise a FunctionSpace with the present
> FunctionSpace constructors.
>
> Garth

A sidenote: If a FunctionSpace is always needed to create a
Function, and this must match the FunctionSpace for a coefficient
when assembling, then a ConstantFunction can't be used as
coefficient to non-DG0 form arguments.

I agree that the requirement that userfunctions have a FunctionSpace
seems very strict. Seems to me it also forces a tighter coupling of
application components.

--
Martin