ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Fri, Apr 24, 2009 at 1:00 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> To get upwinding in a DG formulation of the advection-diffusion eqn with
> the FFC .form language, we used
>
> vector = VectorElement("Lagrange", "triangle", 2)
> scalar = FiniteElement("Discontinuous Lagrange", "triangle", 1)
> constant = FiniteElement("Discontinuous Lagrange", "triangle", 0)
>
> u  = TrialFunction(scalar)
> b  = Function(vector)
> of = Function(constant)
>
> def upwind(u, b):
>   return [b[i]('+')*(of('+')*u('+') + of('-')*u('-')) for i in range(2)]
>
> to return the product b*u, with u taken from the 'upwind' side. How
> should the function 'upwind' look using UFL?

Lets see...

def upwind(u, b):
    s = of('+')*u('+') + of('-')*u('-')
    return [b[i]('+')*s for i in range(2)]

This returns a list, so it's a vector-valued expression?
s is a scalar expression, and b is a vector-valued expression,
so I would simply do

def upwind(u, b):
    s = of('+')*u('+') + of('-')*u('-')
    return b('+')*s

Does that look right?

Martin