ffc team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Anders Logg wrote:
> On Tue, Dec 01, 2009 at 09:41:04AM +0100, Marie Rognes wrote:
>> Anders Logg wrote:
>>> On Tue, Dec 01, 2009 at 09:15:53AM +0100, Marie Rognes wrote:
>>>> Anders Logg wrote:
>>>>> On Mon, Nov 30, 2009 at 11:01:59PM +0000, Garth N. Wells wrote:
>>>>>> Anders Logg wrote:
>>>>>>> We still haven't decided on the correct strategy for choosing the
>>>>>>> degree of an unspecified element.
>>>>>>>
>>>>>>> What we have now looks at the total degree of the form and then sets
>>>>>>> the degree accordingly. This doesn't really work weoull and the reason
>>>>>>> is quite simple: We can't figure out the total degree correctly if we
>>>>>>> don't know the degree of the coefficient.
>>>>>>>
>>>>>>> So my new suggestion is the following. We simply scan all elements in
>>>>>>> the form with specified degrees and set the degree to the maximum
>>>>>>> degree among the elements.
>>>>>>>
>>>>>> Or should it be the maximum degree of the test and trial functions?
>>>>> Yes, that's basically what happens now. It looks at everything that
>>>>> has a degree so it looks at the test and trial functions but also at
>>>>> any coefficients that may happen to have a degree.
>>>>>
>>>>> That's useful for say v*f*g*dx if one of f and g happen to have a
>>>>> degree specified. Then the degree for the other needs to be the same.
>>>>>
>>>> Why?
>>> Since that's how the generated quadrature code works. It loops over
>>> quadrature points for an integrand and then it's useful if everything
>>> in the integrand is evaluated at those points.
>>>
>> Ok.
> 
> I have made a new change of the selection strategy.
> 

Does the change in UFL affect the polynomial degree of the integrand as
computed by UFL?  I see that it's no longer taking into account
derivatives, so if v and u1 are P1, will UFL tell the form compiler that

   dot(grad(v), grad(u))

is zero-order or second-order?


> For quadrature, FFC now looks at the maximum degree of anything in the
> form (including test and trial functions and coefficients).
> 
> For tensor representation, FFC first looks at the maximum degree to
> select the degree but then looks at the total degree to select the
> quadrature it uses at compile time.
> 
> I think this looks ok now and both FFC and UFL are ready for a new
> release. There's still the bug fix Kristian is working on for using
> quadrature elements for coefficients instead of Lagrange, but we
> don't need to wait with the release.
> 

OK.

> FFC is still verbose about its selection of degrees so keep an eye on
> what FFC prints during compilation and report any strange behavior.
>

Yes, good to keep it on initially.

Garth

> --
> Anders
> 
> 
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