ffc team mailing list archive

[Shawn Walker <walker@xxxxxxxxxxxxxxx>]

ok, so I almost have a demo that demonstrates how to roughly implement 
curved triangles.  I checked the code against my own matlab/c++ code for 
the case when the triangles are straight.  I tried this for a mesh of two 
triangles of diameter approx 0.5.  The max error in the matrix entries for 
this straight case is 1.77E-7.  I would have thought it would be smaller, 
but maybe my own code is not the greatest.

Anyway, I also compared the iso-param FFC implementation to my own stuff 
when one triangle is curved.  The error was 1.11.  So something is wrong. 
I think the problem is this.  I cannot simply change

Jinv_00 ---> NEW_Jinv_00[ip]

In the formula that FFC generates.  Because that quad formula is dependent 
on the jacobian being constant.  I think.  Is this correct?

- Shawn

On Mon, 22 Jun 2009, Anders Logg wrote:

> I think Shawn just wants to get the quadrature points so he can
> hand-modify the code for tabulate_tensor to handle higher-order mapped
> elements (to make a prototype for higher-order elements).
>
> Correct me if I'm wrong.
>
> In that case, we won't need to make them available since they are
> available to the form compiler when the code is being generated, but
> it would help if they were available in a comment in the generated code.
>
> --
> Anders
>
>
> On Mon, Jun 22, 2009 at 10:28:29PM +0200, Martin Sandve Alnæs wrote:
> > On Mon, Jun 22, 2009 at 9:10 PM, Kristian
> > Oelgaard<k.b.oelgaard@xxxxxxxxxx> wrote:
> > > Quoting Shawn Walker <walker@xxxxxxxxxxxxxxx>:
> > >
> > > > Actually, I am still a little confused.  Whenever you compute an integral
> > > > by quadrature, you need to evaluate the integrand at the quadrature
> > > > points.  Those are the points I need.
> > >
> > > If you have a quadrature element in your form
> > >
> > > element = FiniteElement("Quadrature", triangle, 2)
> > >
> > > you can call the
> > > tabulate_coordinates() function of the dof_map associated with the quadrature
> > > element. If you don't have a quadrature element there is no direct way of
> > > getting the quadrature points.
> > >
> > > > I just need the quad rule that is used in a particular case.  I see the
> > > > weights are defined in the tabulate_tensor routine.  Are the points listed
> > > > in a comment somewhere?
> > >
> > > No, currently not. But it might be a natural thing to have. I'll look into it.
> >
> > It could be an idea to make it available through UFC,
> > but then again each ufc::*_integral may use different
> > quadrature rules for different terms...
> > However, an exception can be thrown if there is no unique rule in use.
> >
> > Martin
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