ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Sun, Apr 19, 2009 at 2:48 PM, Anders Logg <logg@xxxxxxxxx> wrote:
> On Sun, Apr 19, 2009 at 02:02:57PM +0200, Martin Sandve Alnæs wrote:
>> With some renaming, we now have:
>>
>> extract_max_quadrature_element_degree:
>> Returns max degree of found quadrature elements, None with no
>> quadrature elements
>
> Sounds good.
>
>> estimate_quadrature_degree:
>> Uses the formula 2*v.element().degree() for linear forms,
>> v.element().degree()+u.element().degree() for bilinear forms,
>> don't know if we need this? Returns None for functionals now.
>> The form compilers could have an option to use this variant.
>
> Is it to be used as a fallback if the others fail?

No, from what I understand this is the default in e.g. Diffpack,
and may often be sufficient? I don't know the conditions for this.
I was thinking that we can give the choice between the two
approaches to the user through options to the form compilers.

Kent, what do you say?

>> estimate_max_polynomial_degree:
>> Estimates the highest polynomial degree of the expression.
>> It is an estimate since not all operators are polynomials.
>
> Does it return something sensible even if the expression is not a
> polynomial?

Yes, the default rule for unhandled types are to return the max
degree of the operands, so the degree of exp(f**2) will be the
same as the degree of f**2. We could define heuristic rules like
degree(exp(f)) -> 2*degree(f), if that makes any sense.

> If so, then estimate_quadrature_degree may not be needed.
>
> It would be enough for a form compiler to do this:
>
>  quadrature_degree = extract_max_quadrature_element_degree(integral)
>  if quadrature_degree is None:
>      quadrature_degree = estimate_max_polynomial_degree(integral)
>
> Perhaps this should be in UFL?

As I said above, I think this should be controllable by form compiler options,
so in that case no. Also, Kristian wants splitting of expression terms
by polynomial degree in the future, which will be yet another way to
handle this.

Martin