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["Garth N. Wells" <gnw20@xxxxxxxxx>]

Andy Ray Terrel wrote:
> Hello,
>
> I'm still getting a hang of this but I was trying to do some things
> with mixed elements and derivatives.  I'm not sure if I have the bug
> or if ufl has a bug but the following doesn't pass ufl-analyse.
>
>
> sElem = TensorElement("DG", triangle, 1)
> vElem = VectorElement("CG", triangle, 2)
>
> mElem = sElem + vElem
>
> phi, v = TestFunctions(mElem)
> sigma, u = TrialFunctions(mElem)

The above is the problem. You need to use 'split'. Look at the 
cahn-hilliard demo for an example of how to do it.

Garth

> sF = Function(sElem)
>
> f = inner(sF, dot(u, grad(sF)))*dx
> F = derivative(f, sF, phi)
> J = derivative(F, sF, sigma)
>
>
> It seems that the TestFunctions function doesn't return a proper
> TestFunction but a list of things. I can do the following but then I
> loose the mixed element, which I don't know if ffc could handle.
>
>
> sElem = TensorElement("DG", triangle, 1)
> vElem = VectorElement("CG", triangle, 2)
>
> mElem = sElem + vElem
>
> phi = TestFunction(sElem)
> v = TestFunction(vElem)
> sigma = TrialFunction(sElem)
> u = TrialFunction(vElem)
>
> sF = Function(sElem)
>
> f = inner(sF, dot(u, grad(sF)))*dx
> F = derivative(f, sF, phi)
> J = derivative(F, sF, sigma)
>
>
> Any thoughts on either my bug or ufl please let me know.
>
> -- Andy
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