dolfin team mailing list archive

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

2008/11/4 Johan Hake <hake@xxxxxxxxx>:
> On Tuesday 04 November 2008 15:00:42 Martin Sandve Alnæs wrote:
>> 2008/11/4 Johan Hake <hake@xxxxxxxxx>:
>> > On Tuesday 04 November 2008 13:59:22 Martin Sandve Alnæs wrote:
>> >> 2008/11/4 Johan Hake <hake@xxxxxxxxx>:
>> >> > On Tuesday 04 November 2008 13:07:07 Martin Sandve Alnæs wrote:
>> >> >> 2008/11/4 Johan Hake <hake@xxxxxxxxx>:
>> >> >> > Hello!
>> >> >> >
>> >> >> > I have started the work on the PyDOLFIN. We can now define the
>> >> >> > forms in the poisson demo, using the syntax previously discussed,
>> >> >> > see python poisson demo.
>> >> >> >
>> >> >> > A FunctionSpace now inherits both dolfin::FunctionSpace and
>> >> >> > ffc.FiniteElement, and it can be used to instantiate user defined
>> >> >> > Functions which can be used to define forms.
>> >> >> >
>> >> >> > We need to discuss how to implement a discrete function. This is a
>> >> >> > bit complicated using the metaclass magic that is implemented now.
>> >> >> > Now we cannot do:
>> >> >> >
>> >> >> >  u = Function(V)
>> >> >> >  x = u.vector()
>> >> >> >
>> >> >> > as Function is just a dummy class for creation of userdefined
>> >> >> > functions.
>> >>
>> >> I don't quite understand the problem here.
>> >> Are you saying that type(u) is not a subclass of cpp_Function or what?
>> >
>> > With the metaclass implementation, Function cannot inherit cpp_Function
>> > or ffc.Function. A derived class of Function will inherit Function,
>> > cpp_Function and ffc.Function though. Function is as it is now, only an
>> > more or less empty class that can be inherited.
>> >
>> > The syntax above can be valid with some __new__ magic in Function,
>> > probably much in line with what you had in mind.
>>
>> But in the metaclass __new__ function you have explicit control of the
>> bases of the new class you're building, so where's the problem?
>> Just set bases = (cpp_Function, ufl.Function).
>
> Of course. When I wrote the code I never intended Function to be instantiated.

Sure. With the new Function design that will of course happen all the time.

> Would it make sense to always create a Function that is discrete when we just
> write, u = Function(V)?

Yes, just like cpp_Function(V). Anything else would be insane :-)

By the way, this gives a segmentation fault:

from dolfin import *
mesh = UnitSquare(2,2)
V = FunctionSpace(mesh, "CG", 1)
u = cpp_Function(V)
v = u.vector()

Happy debugging :-/

--
Martin