Question #123984 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/123984
Status: Answered => Open
Dominique is still having a problem:
Johan,
Thanks for the pointer. I had looked at the hyperelasticity demo. I
should have called my post "Second derivatives of a weak form". In the
hyperelasticity demo, the weak form is L(v,u)=0 and that is only
differentiated once. What I'd like to do is differentiate the result
once more. If I try
d2u = TrialFunction(V)
da = derivative(a, u, d2u)
print assemble(da, mesh=mesh)
in the hyperelasticity demo, I get the same error as in my initial
message.
In my test example above, a(v,u)=0 is a weak form. Differentiating it
once is OK, but what is the trick to compute second derivatives?
If I'm missing your point, I'm sorry but could you please explain what
is wrong in my example? I'm expecting to obtain a tensor of order 3, or
a collection of matrices. I may not be going about it in the right way.
Thanks!
Dominique
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