dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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.

Garth


> --
> Anders
> 
> 
> 
> 
> 
>> 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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