dolfin team mailing list archive

[Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx>]

On 28 January 2011 12:53, Anders Logg <logg@xxxxxxxxx> wrote:
> B1;2600;0cOn Fri, Jan 28, 2011 at 12:10:30PM +0100, Andre Massing wrote:
>> Den 28.01.11 12.06, skrev Anders Logg:
>> >On Fri, Jan 28, 2011 at 11:25:27AM +0100, Andre Massing wrote:
>> >>Den 28.01.11 00.30, skrev Anders Logg:
>> >>>On Thu, Jan 27, 2011 at 11:10:08PM +0100, Anders Logg wrote:
>> >>>>I would like to add factory functions in UFC, in particular
>> >>>>
>> >>>>   finite_element* finite_element::create() const;
>> >>>>   dof_map* dof_map::create() const;
>> >>>>
>> >>>>Are there any objections to this? It would be easy to add and easy to
>> >>>>implement in FFC.
>> >>>>
>> >>>>I need it to implement refinement of FunctionSpaces in DOLFIN where
>> >>>>fresh copies of ufc::finite_element and ufc::dof_map are needed given
>> >>>>a ufc::finite_element or ufc::dof_map.
>> >>>>
>> >>>>An alternative is to hack create_sub_foo so that it returns a copy of
>> >>>>the element/dofmap itself if the component argument 'i' is>= the
>> >>>>number of sub elements/dofmaps.
>> >>>
>> >>>I suggest we add this to UFC 1.6 and make a release next week together
>> >>>with DOLFIN 0.9.10, FFC 0.9.5 + other packages that need release. The
>> >>>sooner the better: there will be time to make bug fix releases and
>> >>>things will be tested before 1.0 in March.
>> >>>
>> >>>If there are any other things we want to add to UFC, now's a good
>> >>>time.
>> >>
>> >>What about the tabulate_tensor function taking arguments for runtime
>> >>quadrature rules, as we discussed a while ago? ATM I hacked UFC and
>> >>my generated form files having an additional function
>> >>
>> >>virtual void tabulate_tensor(double* A,
>> >>                              const double * const * w,
>> >>                              const ufc::cell&  c,
>> >>                         dolfin::uint num_quad_points,
>> >>                         const double * const * coordinates,
>> >>                         const double * weights) const
>> >>
>> >>Such an interface would add a flexible layer for those who wants to
>> >>have some type of runtime quadrature.
>> >>
>> >>General opinons about that?
>> >
>> >The question is when this function will be implemented by form
>> >compilers.
>> >
>> >We could add it and let FFC generate an empty function with throws an
>> >exception.
>>
>> So I would like to delegate the following questions to the FFC
>> experts: How difficult would it be to generate code for that?
>
> I assume it would not be very difficult, but it would need to be
> implemented by Kristian (as part of the quadrature code generator) and
> he might have other things to do at the moment.

How difficult it will be depend on what we want the code to do.

1)
If the quad coordinates (arguments) are defined on the reference element, we can
implement https://blueprints.launchpad.net/ffc/+spec/evaluate-basis-reference
and have a small block of code
in the beginning of tabulate_tensor which fills the Psi_* tables with
basis function values (opposed to tabulating them
at FFC compile time which is done now).
Then remainder of the code will not need to change, so this should be
relatively simple.

2)
If the quad coordinates are defined on the physical element, we can
have a small piece of code which maps them to the reference element
and proceed with 1). This is of course a little more work, but maybe
this is the preferred interface (physical coordinates)?

3)
If the quad coordinates are defined on the physical element, we call
the evaluate_basis* functions as is, but then we need to generate
different code to evaluate the element tensor since we get the 'real'
v.dx(0) values (no need to map using K_00 etc.).
This approach will require the most work.

I'm not sure which one will result in the best runtime performance
since a mapping or coordinates will take place somewhere in the code
for all 3 approaches. However, since the current evaluate_basis
involves a mapping physical-->reference-->physical I suspect it to be
the slowest.

Or maybe you had something different in mind?

Kristian

> --
> Anders
>
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