dolfin team mailing list archive

["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.
> > > > 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 ;).

Garth


> Kristian?