ufl team mailing list archive

[Florian Rathgeber <florian.rathgeber@xxxxxxxxxxxxxx>]

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On 24/05/11 14:31, Martin Sandve Alnæs wrote:
> On 24 May 2011 11:39, Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx> wrote:
>> On 24 May 2011 11:23, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
>>> On 23 May 2011 12:05, Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx> wrote:
>>>> On 23 May 2011 11:20, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
>>>>> Is this documented somewhere? Since it is a UFL argument, it should be
>>>>> documented in UFL.
>>>>
>>>> It's not documented anywhere I think. True, it is a UFL argument, but
>>>> UFL doesn't know anything about quadrature schemes and I don't think
>>>> it needs to. The argument just has to be a string, then it's up to the
>>>> form compilers how to deal with the argument.
>>>> FFC currently supports two different schemes, the 'default' scheme
>>>> which is the hardcoded quadrature schemes which Garth implemented and
>>>> the 'canonical' scheme which is a Gauss--Legendre--Jacobi quadrature
>>>> scheme mapped onto simplices.
>>>
>>> Ok. And why does a FiniteElement need to have an associated a quad scheme?
>>
>> Because the dofs of quadrature elements are located at the quadrature
>> points with a value of 1 at those points and zero elsewhere.
>> Derivatives are not defined. This enables this type of element to be
>> handled like any other finite element by the form compilers.
>> However, it also means that FiniteElement("Quadrature", triangle, 2)
>> will have 4 dofs if the 'canonical' scheme is used and only 3 dofs if
>> the 'default' scheme is used.
>> Therefore the scheme has to be included when identifying unique elements.
> 
> Thanks, that makes perfect sense.

Kristian, could you provide an example how this is used? I have a use
case where I want to specify a quadrature scheme and this would come in
really handy. However I don't currently see how to access this
information in the form compiler.

Florian
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