ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On 30 May 2011 21:39, Anders Logg <logg@xxxxxxxxx> wrote:
> How is this mapping created? Which degree is chosen for the elements?
> If it's the same as currently used in FFC, we can drop that and rely
> on UFL.

It only adds missing cells. I think which degrees to choose is not
something UFL should guess at, that is completely in the form
compiler realm. In particular I think FFC should choose quadrature
elements for quadrature representation and CG elements for tensor
representation, which are concepts we do not want to introduce in UFL.

But the original bug report here was that FFC does not pass any
element mapping at all, so if you need to map degrees you should
look into that.

> Here's what's used in FFC:
>
>  # Extract common degree
>  common_degree = max([e.degree() for e in elements])
>  if common_degree is None:
>      common_degree = default_quadrature_degree
>
>  # Degree must be at least 1 (to work with Lagrange elements)
>  common_degree = max(1, common_degree)

So if f and v are CG2 functions, then f*v*dx which is an up to
4th degree polynomial, is integrated with 2nd degree accuracy?

Martin


> --
> Anders
>
>
> ---------- Forwarded message ----------
> From: "Martin Sandve Alnæs" <785143@xxxxxxxxxxxxxxxxxx>
> To: logg@xxxxxxxxx
> Date: Mon, 30 May 2011 11:35:32 -0000
> Subject: [Bug 785143] Re: Element mapping is not provided to ufl.Form.compute_form_data()
> In an upcoming commit, the element mapping is now constructed
> automatically by ufl in preprocess in the case of invalid cells. Thus
> ffc (and sfc) do not need to pass a mapping unless you want to override
> things like degree and family.
>
> Note that there may still be issues with the above code snippet, but
> I'll close this bug and report eventual other bugs separately if
> necessary.
>
> ** Changed in: ffc
>       Status: Confirmed => Invalid
>
> --
> You received this bug notification because you are a member of FFC Core
> Team, which is subscribed to FFC.
> https://bugs.launchpad.net/bugs/785143
>
> Title:
>  Element mapping is not provided to ufl.Form.compute_form_data()
>
> Status in FEniCS Form Compiler:
>  Invalid
>
> Bug description:
>  FFC does not provide an element mapping to
>  ufl.Form.compute_form_data(). This is needed when used from PyDOLFIN,
>  to make forms well defined when coefficients are missing cells.
>
>  I have some failing code, will need to simplify it before I post it
>  here.
>
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