dolfin team mailing list archive

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

Quoting "Garth N. Wells" <gnw20@xxxxxxxxx>:

>
>
> Anders Logg wrote:
> > On Fri, Apr 17, 2009 at 03:57:09PM +0800, Garth N. Wells wrote:
> >>
> >> Anders Logg wrote:
> >>> On Fri, Apr 17, 2009 at 03:07:17PM +0800, Garth N. Wells wrote:
> >>>> Anders Logg wrote:
> >>>>> On Fri, Apr 17, 2009 at 08:59:43AM +0200, Johan Hake wrote:
> >>>>>> On Friday 17 April 2009 03:32:26 Garth N. Wells wrote:
> >>>>>>> Should we start moving to UFL-based forms for the DOLFIN demos? Is
> the
> >>>>>>> only serious outstanding issue on the FFC side the correct
> determination
> >>>>>>> of the quadrature order?
> >>>>>> Not sure how this could be best done in PyDOLFIN.
> >>>>>>
> >>>>>> We could add
> >>>>>>
> >>>>>>   from dolfin.ufl import *
> >>>>>>
> >>>>>> after each
> >>>>>>
> >>>>>>   from dolfin import *
> >>>>>>
> >>>>>> in the demos. When this is done and it all just works(TM) we can move
> the
> >>>>>> files in the site-packages/dolfin/ufl directory down to
> site-packages/dolfin,
> >>>>>> and remove
> >>>>>>
> >>>>>>   from dolfin.ufl import *
> >>>>>>
> >>>>>> from the demos?
> >>>>>>
> >>>>>> Johan
> >>>>> I suggest we just move everything to UFL at once and then solve any
> >>>>> problems that we encounter.
> >>>>>
> >>>>> I'm intending to remove the .form support from FFC quite soon (maybe
> >>>>> today).
> >>>>>
> >>>>> It's easier to fix things so that they work with UFL than to have two
> >>>>> conflicting form languages work at the same time.

I agree on this.

> >>>> The quadrature issue is serious, so I think that it should be tackled
> >>>> before the transition, or at least a short-term plan for how to solve it
> >>>> should be in place.
> >>>>
> >>>> Garth
> >>> Is it so serious? It's a small thing compared to what will happen when
> >>> the .form support is removed from FFC (as in everything will be broken
> >>> until fixed).
> >>>
> >> Results computed with the new and old formats will not, in general, be
> >> the same, so I considered it to be serious.
> >
> > Yes, they won't be the same but I thought they would still be correct
> > (as in possibly using a better quadrature rule than needed).
> >
>
> No, it uses a lower degree of quadrature. For example, for the Poisson
> demo using the new UFL format only one quadrature point is used for the
> source term, whereas enough points for a quadratic polynomial are required.
>
> Not quite sure what 'not the same but still correct' means ;).

As far as I can tell the current implementation in UFL will result in a
sufficient degree of quadrature being used.

Kristian

> Garth
>
>
> > Kristian?
> >
>
>
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