Subject: [Ffc] ElementUnion

From: Marie Rognes <[email-masked]>
Date: Mon, 08 Mar 2010 12:01:31 +0100

[email-masked] wrote:
> ------------------------------------------------------------
> revno: 1440
> committer: Marie E. Rognes <[email-masked]>
> branch nick: ffc
> timestamp: Sun 2010-03-07 21:32:00 +0100
> message:
>   Bug fixes in logic wrt unions of mixed elements. Human-readable code
>   generated for Mini looks correct now :)
>   
>   (Don't know about evaluate_basis* and tabulate_tensor*)
>   

FFC is now able to compile ElementUnions. An ElementUnion of a set
of elements represents the span of the union of the finite element bases.
A classic example of its use would be to augment some element space
by the bubble element (cf ffc/demo/Mini.ufl).

Note that it is not really a finite element in the Ciarlet sense,
because the combined basis does not form a nodal basis.
In short, the effect is that one can assemble forms, but
interpolation onto such spaces is not safe.

Some comments:
(a) I'm not convinced that ElementUnion is the perfect name.
(b) Some additions are required for pydolfin to recognize ElementUnions. 
Hake?
(c) It is not fully tested -> hangs on (b)

--
Marie