dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Apr 11, 2007 at 06:15:30PM +0200, Garth N. Wells wrote:
> Anders Logg wrote:
> > On Tue, Apr 10, 2007 at 06:14:12PM +0200, Garth N. Wells wrote:
> >> Connected to Kristian's work on quadrature in FFC, we should think about 
> >> how to work with functions which do not come from a finite element 
> >> space. Such functions (like stress for a plasticity model or viscosity 
> >> for a non-Newtonian flow) are evaluated at quadrature points, rather 
> >> than at nodes.
> >>
> >> Garth
> > 
> > The current design (including UFC) assumes that all functions can be
> > interpolated to a finite element basis, but I think it will work for
> > the quadrature code generation to imagine that you have a finite
> > element basis where the quadrature points are the same as the nodes.
> > (But you never need to know the basis functions.)
> > 
> > The array of coefficients (double** w) that comes in to the function
> > tabulate_tensor() should contain the coefficients, but for the
> > quadrature these will be the same as the values at the quadrature
> > points, and this should work out fine since the values that go in to w
> > are decided by the evaluate_dof() function that also gets
> > generated.
> > 
> > So the quadrature code generator just needs to make sure that
> > evaluate_dof() picks the values at the quadrature points.
> >
> 
> The problem with this approach is that it's not possible to create a 
> consistent linearisation when dofs and integration points do not 
> coincide. Kristian and I went through this in detail a while ago.
> 
> Garth

Yes, I remember, but my suggestion was that the dofs and the points
should coincide. Then the linearization should be ok?

/Anders