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[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

I'll take a look at improving the error message and checking,
but try this (if I understand what you're trying to do correctly):

kc = Function(mixed_element)
k1, c1 = split(kc)
dkc = TrialFunction(mixed_element)
dk, dc = split(dkc)

...
a1 = derivative(L1, kc, dkc)

Martin



On Sat, Jun 6, 2009 at 10:34 PM, Garth N. Wells<gnw20@xxxxxxxxx> wrote:
> I've used the UFL automatic differentiation for a primal problem, and it
> worked great. Now I'd like to try it for the Cahn-Hilliard demo which is
> a mixed method. I'd like to do:
>
>    a1 = derivative(L1, k1, dk) + derivative(L1, c1, dc)
>
> but I get the below error. Is there are trick for mixed elements?
>
> Garth
>
>
>
> Traceback (most recent call last):
>   File "/usr/local/bin/ffc", line 186, in <module>
>     sys.exit(main(sys.argv[1:]))
>   File "/usr/local/bin/ffc", line 130, in main
>     execfile(script, {})
>   File "CahnHilliard2D.py", line 68, in <module>
>     a1 = derivative(L1, k1, dk) + derivative(L1, c1, dc)
>   File "/usr/local/lib/python2.6/dist-packages/ufl/formoperators.py",
> line 142, in derivative
>     functions, basis_functions = _handle_derivative_arguments(function,
> basis_function)
>   File "/usr/local/lib/python2.6/dist-packages/ufl/formoperators.py",
> line 128, in _handle_derivative_arguments
>     functions       = Tuple(*functions)
> UnboundLocalError: local variable 'functions' referenced before assignment
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