ffc team mailing list archive

[Kristian Oelgaard <k.b.oelgaard@xxxxxxxxxx>]

Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:

> In principle UFL isn't concerned with integration method,
> since this is the main difference between the form compilers.

I think it would make sense if UFL would compute the degree of a monomial, and
attach it as a member. Then the compilers could just ask for this info and
generate the proper integration rule (potentially user specified)

> But we need this functionality in both form compilers,
> so it should be implemented properly in ufl.algorithms
> at some point.

> Martin
> 
> 
> 
> On Fri, Dec 12, 2008 at 11:41 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> > I guess it's the following code in monomialtabulation.py that causes
> > this:
> >
> > def __compute_degree(basisfunctions):
> >    "Compute total degree for given monomial term."
> >    q = 0
> >    for v in basisfunctions:
> >        q += v.element.degree()
> >        for d in v.derivatives:
> >            q -= 1
> >    return q
> >
> >
> > It just looks at v.element.degree() which for a mixed element returns
> >
> > def degree(self):
> >    "Return degree of polynomial basis"
> >    return max([element.degree() for element in self.__elements])
> >
> >
> > So it's a feature/bug. We would need to modify _compute_degree so that
> > it calls a new function v.degree() which would look at the element for
> > that specific component.

OK, we'll need to fix this in both monomialtabulation.py and monomialintegration.py.

Kristian


> > --
> > Anders
> >
> >
> > On Fri, Dec 05, 2008 at 05:39:23PM +0100, Kristian Oelgaard wrote:
> >>
> >> Hi,
> >>
> >> I stumbled over the following which seems peculiar to me:
> >>
> >> P2 = VectorElement("Lagrange", "triangle", 2)
> >>
> >> DG = FiniteElement("Discontinuous Lagrange", "triangle", 0)
> >>
> >> ME = MixedElement([P2, DG])
> >>
> >>
> >>
> >>
> >> (v, q) = TestFunctions(ME)
> >>
> >> (u, p) = TrialFunctions(ME)
> >>
> >>
> >>
> >>
> >> a = q*p*dx
> >>
> >>
> >> Now, FFC insists that the degree of the above form is 4 and it will
> therefore
> >> use 3x3 integration points. For tensor representation this will lead to
> an
> >> increase in FFC compile time, for quadrature an increase in runtime.
> >>
> >> Is this a bug? Or something that happens for a good reason and which is
> hard to
> >> do anything about? What will UFL do?
> >>
> >> Kristian
> >>
> >>
> >> _______________________________________________
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> >> FFC-dev@xxxxxxxxxx
> >> http://www.fenics.org/mailman/listinfo/ffc-dev
> >
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