ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

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.

Martin