ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On 27 April 2011 15:49, Anders Logg <logg@xxxxxxxxx> wrote:

> 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.
>

1) You don't know who else may have references to those objects. All bets
are off.

2) You change the hash of the objects. That messes up dicts and sets that
have them as keys. Severly.

3) The hack to update the repr of the objects isn't working, because
expressions that reference them may have their own cached repr strings which
won't get updated. Even if that wasn't a problem, dicts and sets would be
messed up by the changed hashes anyway.

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?


Wouldn't change any of the above reasons.

Martin


>
> --
> 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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> > >
> >
>