Agreed.
> We could
> estimate the quadrature scheme when test/trial functions are present,
Why not also raise an exception here? How to estimate?
--Nico
On Tue, Aug 26, 2014 at 10:50 AM, Garth N. Wells <gn...@cam.ac.uk> wrote:
> To summarise this thread, it seems we need to introduce the concept of an
> 'Expression' that can be evaluated at arbitrary points. It should not be a
> Quadrature{Element/Function} because the proposed object could be used in
> different forms with different evaluation points. The follow-on on issue is
> then how a 'point-wise' expression should be treated in forms. We could
> estimate the quadrature scheme when test/trial functions are present, and in
> the case of functionals throw an error if the user doesn't supply the
> quadrature degree.
>
> If this is the consensus, we can add an issue(s) to Bitbucket. Please reply
> with feedback.
>
> Garth
>
>
>
> On Fri, 15 Aug, 2014 at 9:27 AM, Martin Sandve Alnæs <marti...@simula.no>
> wrote:
>>
>> On 14 August 2014 11:09, Martin Sandve Alnæs <marti...@simula.no> wrote:
>>>
>>> On 14 August 2014 10:38, Garth N. Wells <gn...@cam.ac.uk> wrote:
>>>>
>>>> I favour (a) explicit provision of the element/function space; or (b)
>>>> evaluation at quadrature points with errors for cases where no data is
>>>> available for deciding on a sensible quadrature scheme. Using quadrature
>>>> points would fix some other awkward issues, like specifying boundary
>>>> conditions on polygon faces which 'creep' around corners is subdomains are
>>>> not marked.
>>>
>>>
>>>
>>> I agree with both (a) and (b).
>>
>>
>> I see I was a bit quick there.
>>
>> I favour evaluation at quadrature points for cases where no
>> element/function space is provided, combined with making the choice of
>> quadrature degree/scheme easier accessible with dx(degree=3) notation. Maybe
>> we can add in a "Warning: automatic selection of integration degree 3, this
>> may be inexact.".
>>
>> The quadrature degree estimation is just that: an _estimation_. It is not
>> exact for any non-polynomial expressions. If we want to throw an error when
>> the degree for exact integration cannot be determined, that is a partially
>> separate issue from this one, and it will break a lot of programs. If we
>> want integration involving any Expression without an element to be
>> guaranteed exact, we will need to require the integration degree to be set
>> explicitly. This will probably break every single dolfin demo.
>>
>> Martin
>
>
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