ufl team mailing list archive

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

Kristian Oelgaard wrote:
> 
> 
> On 30 January 2010 15:11, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>>
>>
>> Kristian Oelgaard wrote:
>>>
>>>
>>> On 30 January 2010 11:56, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>>>> In the UFL manual, there is a section on 'conditionals' (sec 2.11) but
>>>> I'm unsure of the what the intention is. Is the idea that they can be
>>>> used in forms? It would be really useful if I could do something like:
>>>>
>>>>  un   = dot(u, n)
>>>>  cond = lt(un, 0.0)
>>>>
>>>> and use 'cond' (= 0 or 1) in a form.
>>>
>>> As I recall it, we (you and I) thought it would be nice to have
>>> conditionals so we could use it to determine if a facet was an outflow
>>> facet or not at runtime in the generated C++ code. I think the idea was
>>> to simply translate the conditionals in a form into
>>>
>>> if ( condition )
>>> {
>>>  do something
>>> }
>>> blocks in the generated code.
>>> However, due to other improvements in the UFL language we can now
>>> determine the outflow facets in a more elegant way, in my opinion,
>>
>> The problem is that it doesn't generalise well to time-dependent
>> problems. I would like to a function that can return the sign of a
>> function.
> 
> ... which is one of the cases where conditionals will be useful. :) My
> best guess is that they will not be supported in the upcoming release of
> FFC, but maybe 0.9.3? You can add a blueprint to FFC, I think it should
> work on the UFL side?
>

I'm not sure that it's working on the UFL side.

Garth

> Kristian
> 
>> Garth
>>
>>> so we
>>> didn't look further into the conditionals. That being said, there might
>>> be other cases where it will still be useful.
>>>
>>> Kristian
>>>> Garth
>>>>
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>>>
>>
>>
>>
>