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[Garth Wells <question102159@xxxxxxxxxxxxxxxxxxxxx>]

Question #102159 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/102159

    Status: Open => Answered

Garth Wells proposed the following answer:
On Thu, 2010-02-25 at 11:28 +0000, Richard Norton wrote:
> Question #102159 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/102159
> 
>     Status: Answered => Open
> 
> Richard Norton is still having a problem:
> Sorry... in mathematical terms, sigma is a vector field from R^2 to R^2.
> It maps (a,b) to (a,2(b^2-1)b) for real numbers a and b.   So yes,
> sigma_1 and sigma_2 are the two components of sigma.  I want to define
> an expression or function (called "sigma") so that the following code
> makes sense...
> 

Try this:

  # Test and trial functions
  v = TestFunction(V)
  u = TrialFunction(V)
  uold = Function(V)

  def sigma(u):
      return as_vector( [u.dx(0), 2*(u.dx(1)**2 -1)*u.dx(1)] )
	
  # Variational problem
  a = dot(grad(u), grad(v))*dx
  L = dot(sigma(uold),grad(v))*dx

Garth


> 
> 
> 
> # Test and trial functions
> v = TestFunction(V)
> u = TrialFunction(V)
> uold = Function(V)
> 
> def sigma(gradu):
>     ????
> 	
> # Variational problem
> a = dot(grad(u), grad(v))*dx
> L = dot(sigma(grad(uold)),grad(v))*dx
>

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