Weakform of nonlinear equation

On Fri, Mar 26, 2010 at 10:11:24PM -0000, Jack wrote:
> New question #105644 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/105644
>
> Dear all
>
> How can I represent this pde using ufl.
>
> -d/dx(du/dx) - 2u*du/dx = 0
>
> I'm having trouble particularly with 2u*du/dx.
>
> Thanks
>
> Jack

Does it not work if you write 2*u*u.dx(0)*dx?

--
Anders

Thanks Anders Logg, that solved my question.

Thanks Anders.

I just spotted that ffc -l dolfin Nonlinear.ufl gives this error at the end:

Compiler stage 2: Computing intermediate representation
-------------------------------------------------------
  Computing representation of 1 elements
  Computing representation of 1 dofmaps
  Computing representation of integrals
  Computing tensor representation
  Extracting monomial form representation from UFL form
  Transforming monomial form to reference element
  Precomputing integrals on reference element
  Precomputing integrals on reference element
Unable to extract all indices.

*** FFC: Unable to extract all indices.
*** FFC: To get more information about this error, rerun FFC with --debug.

This is what I have in my UFL form file

element = FiniteElement("Lagrange", "interval", 2)

v = TestFunction(element)
du = TrialFunction(element)

u = Coefficient(element)

L = inner(grad(v), grad(u))*dx - 2*u*u.dx(0)*dx
a = derivative(L, u, du)

Thanks

Jack

I forgot to multiply the second term by the TestFunction.