ufl team mailing list archive

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

On 30 January 2010 15:11, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> Kristian Oelgaard wrote:
> > On 30 January 2010 11:56, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> > > In the UFL manual, there is a section on 'conditionals' (sec 2.11) but
> > > I'm unsure of the what the intention is. Is the idea that they can be
> > > used in forms? It would be really useful if I could do something like:
> > >
> > >  un   = dot(u, n)
> > >  cond = lt(un, 0.0)
> > >
> > > and use 'cond' (= 0 or 1) in a form.
> >
> > As I recall it, we (you and I) thought it would be nice to have
> > conditionals so we could use it to determine if a facet was an outflow
> > facet or not at runtime in the generated C++ code. I think the idea was
> > to simply translate the conditionals in a form into
> >
> > if ( condition )
> > {
> >  do something
> > }
> > blocks in the generated code.
> > However, due to other improvements in the UFL language we can now
> > determine the outflow facets in a more elegant way, in my opinion,
>
> The problem is that it doesn't generalise well to time-dependent
> problems. I would like to a function that can return the sign of a function.

... which is one of the cases where conditionals will be useful. :) My best guess is that they will not be supported in the upcoming release of FFC, but maybe 0.9.3? You can add a blueprint to FFC, I think it should work on the UFL side?

Kristian

> Garth
>
> > so we
> > didn't look further into the conditionals. That being said, there might
> > be other cases where it will still be useful.
> >
> > Kristian
> > > Garth
> > >
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