ufl team mailing list archive

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

Johan Hake wrote:
> > 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)
>
> I might be totaly of here but does not TestFunctions and TrialFunctions
> return a properly splitted FooFunction?
>
> What I mean is:
>
>   dk, dc = TestFunctions(ME)
>
> should be the same as:
>
>   du = TestFunction(ME)
>   dk, dc = split(du)
>
> Please correct me if I am wrong.

Yes, but former approach doesn't provide access to the 'mother' function 
du, and it's with respect to du that you want to compute the derivative.

Garth


> Isn't the problem the sF Function, which is defined using an element which
> is not 'properly mixed'?
>
> > > 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 think the list you refere to is the somewhat unreadable representation
> of the view of the TestFunctions, which should be the correct one.
>
> Johan
>
> > 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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