dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Apr 27, 2011 at 02:39:17PM +0100, Garth N. Wells wrote:
>
>
> On 27/04/11 14:34, Anders Logg wrote:
> > On Wed, Apr 27, 2011 at 03:24:05PM +0200, Martin Sandve Alnæs wrote:
> >> On 27 April 2011 12:38, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> >>
> >>
> >>
> >>     On 27/04/11 11:08, Kristian  lgaard wrote:
> >>     > On 27 April 2011 11:52, Anders Logg <logg@xxxxxxxxx> wrote:
> >>     >> On Wed, Apr 27, 2011 at 10:40:50AM +0100, Garth N. Wells wrote:
> >>     >>> We need a quick discussion round to resolve this issue - DOLFIN is now
> >>     >>> broken. I guess we need the form compiler to decide on the cell and
> >>     >>> element type, and then have UFL return a new form.
> >>     >>
> >>     >> Yes, Martin mentioned at some point that it would be easy to add such
> >>     >> a function to UFL (that takes a form and replacement elements and
> >>     >> returns a new form).
> >>     >>
> >>     >> Martin, could you add such a function?
> >>
> >>
> >> I started some time before easter, but as Garth says...
> >>
> >>
> >>     > I think ufl.algorithm.transformations.replace would work if
> >>     > FiniteElementBase derived from 'Terminal'.
> >>     > Currently, it derives from 'object', what is the reason for that?
> >>     > Anyway, it should be simple enough to add something equivalent for
> >>     elements.
> >>     >
> >>
> >>     I was thinking that we only need to replace Coefficients, e.g. if a
> >>     Coefficient is defined using an 'incomplete element', FFC can create an
> >>     element, a Coefficient and the perform the replacement. Looks like UFL
> >>     can do this already.
> >>
> >>     The problem from the DOLFIN side is that the new UFL Coefficient will be
> >>     different from the DOLFIN/UFL Coefficient, and would be a
> >>     ufl.Coefficient and not a dolfin.Coefficient.
> >>
> >>
> >> ... this may be a problem. Since I don't really know the motivation for this
> >> feature request, I can't solve this problem for you.
> >
> > The motivation is that we want to accomplish what we now accomplish
> > with the set_cell/degree functions that you have decided to remove.
> >
> > This allows us to write f = Expression("sin(x[0])") and let the form
> > compiler choose a suitable approximation for the expression.
> >
>
> Just to keep the caching discussion alive ;), perhaps a DOLFIN
> Expression (which is a subclass of ufl.Coefficient) with an incomplete
> function space could have a cache ufl.Expressions that have completely
> defined elements, but which share the eval() function of the original. I
> don't know on a technical level how to make this work.
>
> The JIT compiler would need to return a map of replaced -> new coefficients.

I don't really understand why the set_degree/cell functions are so
bad. I understand that a form should be immutable, but if the cell and
degree are set to "?", we're not really changing anything.

Perhaps it would be enough to insert a check in the set_cell/degree
functions that they can only be called on objects where the cell/degree
has not been set?

--
Anders


> Garth
>
>
> >> Martin
> >>
> >>
> >>
> >>
> >>     Garth
> >>
> >>     > Kristian
> >>     >
> >>     >>
> >>     >>
> >>     >>> Garth
> >>     >>>
> >>     >>> On 26/04/11 07:32, noreply@xxxxxxxxxxxxx wrote:
> >>     >>>> ------------------------------------------------------------
> >>     >>>> revno: 1014
> >>     >>>> committer: Martin Aln s <martinal@xxxxxxxxx>
> >>     >>>> branch nick: ufl
> >>     >>>> timestamp: Fri 2011-04-15 21:44:37 +0200
> >>     >>>> message:
> >>     >>>>   Add warnings to set_foo functions in finiteelement.py,
> >>     >>>>   and remove repr modifications after construction time.
> >>     >>>>
> >>     >>>>   If this will break your code, it likely wasn't working
> >>     >>>>   correctly anyway and you need to rewrite it before you
> >>     >>>>   can update to this UFL version.
> >>     >>>>
> >>     >>>>   The set_foo functions will be removed completely before UFL 1.0.
> >>     >>>>
> >>     >>>>   Happy easter holiday :)
> >>     >>>> modified:
> >>     >>>>   ufl/finiteelement.py
> >>     >>>>
> >>     >>>>
> >>     >>>
> >>     >>>
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> >>     >>
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> >>     >>
> >>
> >>
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> >>
> >
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>