ffc team mailing list archive

[Jake Ostien <tostien@xxxxxxxxx>]

Anders Logg wrote:
> On Thu, Jan 10, 2008 at 09:29:56AM -0500, Jake Ostien wrote:
>   
> > Hi,
> >
> > I'd like to write a form based on the lifting operator.  If the lifting 
> > operator (R) is defined as
> >
> >     -\int_Gamma avg(A):jump(B) dS = \int_Omega A:R(B) dV
> >
> > Is there any way I can define a form such as
> >
> >     \int_Omega R(A):R(B) dV
> >
> > Where e.g. A and B are BasisFunctions?
> >
> > I can do this already for a known Function, say H, where I say
> >
> >     V = TestFunction
> >     U = TrialFunction
> >
> >     H = Function
> >
> >     a = dot(V,U)*dx
> >     L = dot(avg(V),jump(H))*dS
> >
> > Then U is the lifted H, projected onto the basis of V.
> >
> > Should this same approach work for BasisFunctions?
> >
> > Jake
> >     
>
> I don't understand what you want to do. The only way I see to compute
> a projection (or lifting) is to define a bilinear form and linear form
> as you do and solve a linear system.
>
>   
Yes, I see.  Here's the problem.  The lifting operator formulation looks 
like
   \int_Omega R(V):R(H) dV

For the R(V) term, I can lift the BasisFunction V and project it to get 
a DiscreteFunction in DOLFIN, but then when I pass in those coefficients 
as arguments to the lifting operator form, how can I tell FFC that those 
coefficients are for the TestFunction?  If I could do this then I could 
just do the projections as a separate step and use the results.

Jake