ufl team mailing list archive

[Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx>]

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.

Kristian

> Martin
>