dolfin team mailing list archive

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

How do you intend to handle (sub)functions in a mixed space?
Currently I don't see how the function space stuff generalizes
to even simple mixed spaces.

Take this simple example in a pure form language (FFC or UFL):
    element1 = VectorElement("CG", "triangle", 2)
    element2 = FiniteElement("CG", "triangle", 1)
    mixed_element = element1 + element2
    f, g = Functions(mixed_element)

Now in PyDOLFIN, would a function space be defined by (reusing the elements):
    space1 = FunctionSpace(mesh, element1)
    space2 = FunctionSpace(mesh, element2)
    mixed_space1 = space1 + space2

or:
    mixed_space2 = FunctionSpace(mesh, mixed_element)

and would the functions in this space be
    f, g = Functions(mixed_space)
or
    fg = Function(mixed_space)
    f, g = fg.sub(0), fg.sub(1)
?

Neither of these two definitions of (f, g) works out.

The syntax
    f, g = Functions(mixed_space)
doesn't work, since ufl.Functions does not return ufl.Function objects,
but ufl.Indexed objects that refer to subexpressions of ufl.Function objects.

The syntax
    fg = Function(mixed_space)
    f, g = fg.sub(0), fg.sub(1)
would require that sub returns something that is a subclass of what
ufl.Functions returns (ufl.Indexed) and at the same time is a dolfin.Function.

--
Martin