Version 2016.1.0, split() for new MixedElement

Question

I have in the past been able to use the syntax

u,v,w = U.split()

to get at the individual components of a 3-way mixed element U.

With version 2016.1.0, split() still works, but now I am confused what is being output. For example, there appears to be a hierarchy of mixed elements now :

from fenics import *

mesh = UnitCubeMesh(2,2,2)
Q    = FiniteElement("CG", mesh.ufl_cell(), 1)
M    = FunctionSpace(mesh, Q*Q*Q)
U    = Function(M)

out  = U.split()
out2 = out[0].split()

v    = out[0]
w    = out[1]
x    = out2[0]
y    = out2[1]

print id(v), id(w), id(x), id(y)

I can't seem to find the documentation on this, can anyone help?

Thanks again,
Evan

EDIT:

To clarify why I need this, I'd like to rename the individual components, and extract their functionspaces. This was possible with the old way and split().

Answer 1

Q*Q*Q means (Q*Q)*Q in Python because * is binary operator. Did you want to do

M    = FunctionSpace(mesh, MixedElement([Q, Q, Q]))

? Then you will get

len(u.split()) == 3

Comments

Ah ha! Yes, perfect, thanks again.