ffc team mailing list archive

[Marie Rognes <meg@xxxxxxxxx>]

On 18. juni 2010 11:38, Kristian Oelgaard wrote:
> On 18 June 2010 01:44, Marie Rognes <meg@xxxxxxxxx> wrote:
>   
>> On 17. juni 2010 15:44, Mehdi wrote:
>>
>> On Wed, 2010-06-16 at 18:04 +0200, Kristian Oelgaard wrote:
>>
>>
>>
>> Mehdi and I discussed this a bit, one way to get around this in FFC is to
>> let
>> VectorElement accept a FiniteElement as argument, then you can do
>>
>> element = VectorElement(V + Q)
>>
>> and still be dimension independent.
>>
>> Or in UFL we can tweak the '+' operator, such that enriching a
>> VectorElement means enriching each of the components of 'self' with
>> the components of 'other'. For this to work the dimension of the two
>> vector elements must of course be identical but I guess that will
>> always be the case, otherwise we throw an error.
>>
>>
>> I will go for this option. This allows us to have simpler code and
>> preserves accessing to the sub-elements of enriched mixed element.
>>
>>
>>
>> How do you plan on handling elements such as the following (relevant in
>> connection with the PEERS element for linear elasticity) with this approach?
>>
>> V = FiniteElement("RT", "triangle", 1)
>> Q = VectorElement("B", "triangle", 3)
>> W = V + Q
>>     
> I was planning on throwing an error :)
>   


Please don't :)

> I did not know that one would ever want to enrich a scalar element
> with a vector bubble function, 

Since RT is a vector-valued element, enriching it with a vector bubble
function
is well-defined.

Strictly speaking, my example is not the enrichment of one UFL VectorElement
with another VectorElement. So, I guess you could overload + for
VectorElement (and TensorElement) only. However, that would make

    V = FiniteElement("CG", "triangle", 1)
    V = V*V
    B = VectorElement("B", "triangle", 3)
    W = V + B

and

    V2 = VectorElement("CG", "triangle", 1)
    W = V2 + B   

behave differently, which I imagine could be rather confusing. 


> but since this appears to be the case
> the only two options, as I see it, are:
>
> 1) do nothing such that one will have to do
>
>   P1 = FiniteElement("Lagrange", tetrahedron, 1)
>   B = FiniteElement("Bubble", tetrahedron, 3)
>   Q = FiniteElement("CG", triangle, 1)
>   Mini = MixedElement([P1 + B], [P1 + B], [P1 + B])*Q
>
> manually.
>
> 2) have VectorElement accept FiniteElementBase as argument to allow
>
>   Mini = VectorElement(P1 + B)*Q
>
> which will reduce the labour of defining elements and still be
> independent of dimensions.
>
>   


Option 2) sounds neat and useful in other contexts too :)


> We could of course try to 'guess' what the user wants but I don't
> think that is a good idea.
>
>   


Agree.

--
Marie


> Kristian
>
>   
>> v = TestFunction(W)
>> u = TrialFunction(W)
>> a = dot(v, u)*dx
>>
>> --
>> Marie
>>
>>
>>
>>
>> Mehdi
>>
>>
>> Kristian
>>
>>
>>
>> Garth
>>
>>
>>
>> Kristian
>>
>>
>>
>> Garth
>>
>>
>>
>>
>>
>> --
>> Marie
>>
>>
>>
>>  Mehdi
>>
>>
>>
>>
>> --
>> Marie
>>
>>
>>
>>
>>
>> Mehdi
>>
>>
>>
>>
>>
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