ffc team mailing list archive

[Marie Rognes <meg@xxxxxxxxx>]

k.b.oelgaard@xxxxxxxxx wrote:
> Hi,
>
> I'm running some tests on evaluate_basis with different elements and 
> here are some results.
>
> The following elements are no longer supported by FIAT:
>  Crouzeix-Raviart and Brezzi-Douglas-Fortin-Marini, will they be 
> supported again?


I would say that BDFM is not important, but that CR is.


> The following elements could not be compiled by gcc because of a 
> problem with and undefined variable 'copy' in evaluate_dof() and 
> evaluate_dofs():
>  FiniteElement('Brezzi-Douglas-Marini', Cell('triangle', 1, Space(2)), 2)
>  FiniteElement('Brezzi-Douglas-Marini', Cell('triangle', 1, Space(2)), 3)
>  FiniteElement('Brezzi-Douglas-Marini', Cell('tetrahedron', 1, 
> Space(3)), 2)
>  FiniteElement('Brezzi-Douglas-Marini', Cell('tetrahedron', 1, 
> Space(3)), 3)
>  FiniteElement('Nedelec 1st kind H(curl)', Cell('triangle', 1, 
> Space(2)), 2)
>  FiniteElement('Nedelec 1st kind H(curl)', Cell('triangle', 1, 
> Space(2)), 3)
>  FiniteElement('Nedelec 1st kind H(curl)', Cell('tetrahedron', 1, 
> Space(3)), 3)

Known potential issue. Will fix.


> A funny thing to note is that
>  FiniteElement('Nedelec 1st kind H(curl)', Cell('tetrahedron', 1, 
> Space(3)), 2)
> compiles fine.
>
> Values differ for the following DG element:
>  FiniteElement('Discontinuous Lagrange', Cell('interval', 1, 
> Space(1)), 2)
>  FiniteElement('Discontinuous Lagrange', Cell('interval', 1, 
> Space(1)), 3)
>  FiniteElement('Discontinuous Lagrange', Cell('interval', 1, 
> Space(1)), 4)
>  FiniteElement('Discontinuous Lagrange', Cell('tetrahedron', 1, 
> Space(3)), 2)
>  FiniteElement('Discontinuous Lagrange', Cell('tetrahedron', 1, 
> Space(3)), 3)
>  FiniteElement('Discontinuous Lagrange', Cell('tetrahedron', 1, 
> Space(3)), 4)
>  FiniteElement('Discontinuous Lagrange', Cell('triangle', 1, 
> Space(2)), 2)
>  FiniteElement('Discontinuous Lagrange', Cell('triangle', 1, 
> Space(2)), 3)
>  FiniteElement('Discontinuous Lagrange', Cell('triangle', 1, 
> Space(2)), 4)
> but Marie changed the ordering of dofs, so that is not big mystery.


I refuse to take the blame for changing the ordering of the dofs! ;)

> I checked some values manually and it looks like the values has just 
> been shifted around so the result should be OK.


Good!


> Values also differ for the following elements:
>  FiniteElement('Nedelec 1st kind H(curl)', Cell('tetrahedron', 1, 
> Space(3)), 2)
>  FiniteElement('Raviart-Thomas', Cell('tetrahedron', 1, Space(3)), 2)
>  FiniteElement('Raviart-Thomas', Cell('tetrahedron', 1, Space(3)), 3)
>  FiniteElement('Raviart-Thomas', Cell('triangle', 1, Space(2)), 2)
>  FiniteElement('Raviart-Thomas', Cell('triangle', 1, Space(2)), 3)
> For the Nedelec element values look the same, but they appear in 
> different places.
>
> If I call tabulate on the FIAT element (reference) I get matching 
> results as when I call evaluate_basis(), so I guess it is OK. Marie, 
> has the ordering of dofs changed for Nedelec?


Don't know actually.  I can check evaluate_dof.


> For the Raviart-Thomas elements the story is almost the same. The only 
> difference is that for e.g.,
>  FiniteElement('Raviart-Thomas', Cell('triangle', 1, Space(2)), 2)
> I get values like '0.44444 0.55556 0.22222 -0.22222 -0.33333' in the 
> 'old' version of FFC and FIAT, but in the new FFC (and the new FIAT) I 
> get values like:
> 0.66667 0.33333 -0.00000 -0.00000 -0.33333' when I tabulate the basis 
> at the same point. Marie, has something changed for RT elements?


Yes. Rob changed the interior degrees of freedom for polynomial degrees 
> 1 from integral moments to point values. Hence the basis
functions have changed.

(Note that there is a unit test for RT2 on a triangle that passes :) )

--
Marie

> For both old and new FFC FIAT.tabulate() and evaluate_basis() agrees 
> so I guess the values are OK.
>
> If the above issues can be confirmed and addressed It looks like 
> evaluate_basis can be trusted.
>
> Kristian
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