ufl team mailing list archive

[Mehdi <m.nikbakht@xxxxxxxxxx>]

On Fri, 2010-06-18 at 12:23 +0200, Kristian Oelgaard wrote:
> On 18 June 2010 12:05, Marie Rognes <meg@xxxxxxxxx> wrote:
> > 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.
> 
> Ha, I completely missed the 'RT', that's what you get for working with
> 'CG' only :)
> Now it makes a lot more sense to me.
> 
> > 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
> 
> Yes, that's what we had in mind, then instead of an error we just
> return an EnrichedElement, then it's up to the user to make sure that
> the enrichment makes sense. I haven't looked at the code in detail
> now, but maybe there are other things we need to check for.
> 
> >    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.
> 
> They do?
> I would expect both instances to end up meaning
> W = MixedElement([FiniteElement('CG', 'triangle', 1) + B]*2)
> 
> or can you spell it out for me?
> 
> >
> >> 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 of course still do this even if we decide on option 1).

Option 2 is also fine with me. Let's see what Garth thinks.

Mehdi

> 
> Kristian
> 
> >
> >> 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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> >>>
> >>>
> >>>
> >>>
> >>>
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> >>>
> >>>
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> >>>
> >>>
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> >>>
> >>>
> >>>
> >
> >