ffc team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Thursday 20 November 2008 00:05:59 Martin Sandve Alnæs wrote:
> 2008/11/19 Johan Hake <hake@xxxxxxxxx>:
> > Hello!
> >
> > We have been discussing to inherit the ffc.{Test,Trial,Basis}Function in
> > dolfin, and instantiate the function with a functionspace instead of an
> > element. Then in assemble.py we extract the functionspaces from the
> > basisfunctions in Formdata (Anders promised this).
> >
> > I had a look in Formdata to try to just extract the basis functions,
> > similare to the coefficients. But the problem is that these functions are
> > not represented in the monomial as the original u and v as they were
> > created by the user.
> >
> > I suppose this is a "feature" of the algrebra in ffc or have I
> > missunderstood it? The function that is used to define the coefficients
> > can be extracted using with c.f, should this be added for the
> > basisfunctions too?
>
> ...
>
> > Will this be an issue in ufl?
>
> Let me think aloud:
>
> - Subclassing BasisFunction (Test and Trial aren't classes) poses no
> problems in itself.

This won't be the case. A dolfin.BasisFunction will inherit 
ufl/ffc.BasisFunction, nothing else. It will have a FunctionSpace.

> - Attaching additional member variables and member functions in this
> class is ok, as long as names don't collide.

Ok. I have added a function_space funciton to extract the FunctionSpace.

> - Implementing any special function "__foo__" other than __init__ in
> the dolfin subclasses may cause trouble. This includes SWIG-generated
> functions, which I think should be ok if the UFL class has precedence
> over the SWIG-generated class in the inheritance list of the PyDOLFIN
> class.

This won't be the case. 

> - BasisFunction and Function objects in a UFL Form are never replaced
> with anything else, exactly with this in mind.

Nice.

> - Algorithms like "J = derivative(-F)", "b = action(a)" which
> introduce additional arguments all have options to explicitly pass the
> BasisFunction or Function to add.

Nice.

> - Retrieving the exact objects used for form arguments from a form
> will be ok, that is the instances of ufl.Function or its PyDOLFIN
> subclass.

Nice.

> I don't see any collisions with this design and ufl.

So, when is it due? ;)

Johan