ufl team mailing list archive

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

Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:

> On Thu, May 14, 2009 at 5:59 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> >
> >
> > Martin Sandve Alnæs wrote:
> >>
> >> On Thu, May 14, 2009 at 9:43 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> >>>
> >>> On Thu, May 14, 2009 at 08:40:41AM +0100, Garth N. Wells wrote:
> >>>>
> >>>> Martin Sandve Alnæs wrote:
> >>>>>
> >>>>> Is there a mathematical difference?
> >>>>>
> >>>> Splitting hairs, I would say yes and that grad(u('+')) is correct and
> >>>> grad(u)('+') is not because grad(u) is not defined in a classical sense.
> >>>> I prefer grad(u('+')), but FFC used to use grad(u)('+'). My preference
> >>>> is however not strong.
> >>>>
> >>>> My immediate question is will the generated code differ for grad(u('+'))
> >>>> and grad(u)('+')?
> >>>>
> >>>> Garth
> >>>
> >>> No, since the restriction will be propagated to the leaves... :-)
> >>
> >> The leaves are terminal expressions, that is literal constants,
> >> geometric quantities, functions and basis functions.
> >> "Propagating to the leaves" means modifying for example
> >>
> >>  (grad(f) + grad(g))('+')
> >
> > So the above works now? It would be super useful for me.
>
> I don't know what FFC does.
>
> But I implemented the propagation right now, only tested
> for a simple case but it's a simple algorithm:
>
> # test_restrictions.py:
> from ufl import *
>
> e = FiniteElement("DG", triangle, 1)
> f = Function(e)
> g = Function(e)
> a = (grad(f) + grad(g))('-')
> print a
>
> from ufl.algorithms import propagate_restrictions
>
> b = propagate_restrictions(a)
> print b
>
>
> martinal@martinal-znote:~/dev/fenics/ufl/sandbox/algorithmtests$
> python test_restrictions.py
> ((grad(w_0)) + (grad(w_1)))('-')
> (grad((w_0)('-'))) + (grad((w_1)('-')))
>
>
> FFC just needs to apply propagate_restrictions to the integrand of
> interior facet integrals.

I just tried it and it appears to be working. However, I got the error:

*** FFC: Not expecting twice restricted expression.
/home/oelgaard/fenics/clone/ffc/scripts/ffc:131: DeprecationWarning:
BaseException.message has been deprecated as of Python 2.6
  error(exception.message)
*** FFC: Not expecting twice restricted expression.
*** FFC: To get more information about this error, rerun FFC with --debug.

for the following form (from Garth)

sigma_a = -b*u - gamma*b*(uhat - u)
sigma_d = kappa*grad(u) + (alpha/h)*kappa*(uhat -u)*n('+')
sigma_i = dot(sigma_a + sigma_d, n)

sigma_plus = sigma_i('+')

a = v('+')*sigma_plus*dS

The reason is that sigma_d already contains n('+'). What should happen in a case
like this? For complex forms it is sometimes easier to declare temporary
expressions and in these cases one might accidentally (or intentionally?)
restrict a function multiple times. Should a restriction just be overwritten or
what would you expect Garth for this form?

Kristian

> Martin
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