dolfin team mailing list archive

[cosby@xxxxxxxxx]

> On Thu, Feb 14, 2008 at 10:06:43AM +0100, Kristen Kaasbjerg wrote:
>> Anders Logg wrote:
>> > On Wed, Feb 13, 2008 at 10:50:23PM +0100, cosby@xxxxxxxxx wrote:
>> >
>> >>>> On Wed, Feb 13, 2008 at 08:49:09PM +0100, Shilpa Khatri wrote:
>> >>>>
>> >>>>> We (Dag and I) are doing this because we would like to have Dolfin
>> >>>>> solve
>> >>>>> the
>> >>>>> Stokes/Navier-Stokes equations as one part of a timestep in our
>> code
>> >>>>> where we
>> >>>>> are moving interfaces that are defined as a random set of points
>> in the
>> >>>>> domain.
>> >>>>>
>> >>>>> Thanks,
>> >>>>> Shilpa
>> >>>>>
>> >>>> Then I suggest first finding out which cells those points lie in,
>> then
>> >>>> then for each cell with a point get the expansion coefficients
>> within
>> >>>> that cell, then multiply those coefficients with the values of the
>> >>>> basis functions at the points.
>> >>>>
>> >>>> The basis functions are available from the ufc::finite_element.
>> >>>>
>> >>>> We can implement a suitable interface for this at some point but
>> >>>> until then, you can do it manually.
>> >>>>
>> >>> Sounds good. Is the GTS_Interface still in place for searching?
>> >>>
>> >>> /Dag
>> >>>
>> >> I'm a little lost here. How is the ufc module used to get hold
>> >> of the basis functions ?
>> >>
>> >> Kristen
>> >>
>> >
>> > You need to get hold of a ufc::finite_element and then call
>> > evaluate_basis_function (see UFC manual). If you have a ufc::form,
>> > then you can create a ufc::finite_element by calling
>> > create_finite_element. If you have a dolfin::Form, then first get the
>> > ufc::form by calling form().
>> >
>> >
>> Ok, so this is doable via the python interface ?
>> In case yes, where is the dolfin::Form then hidden ?
>>
>> Kristen
>
> Yes, you can use it from the Python interface by calling the JIT
> compiler:
>
>   (compiled_form, compiled_module, form_data) = jit(a)
>
> You can then call compiled_form.create_finite_element(i) etc
> since this will be a Python wrapper for a ufc::form.
>
> BUT: If you are using the Python interface, then everything is already
> available through the Python interface, so if you have a
> FiniteElement, you can tabulate it's values at any point by calling
> element.tabulate(). Note that this gives you values on the reference
> element so you need to map the values to the physical element.
>
> Another comment is that things like this are better (more efficiently)
> implemented as C++ components in DOLFIN and then wrapped back to
> Python for general use.

Yes, I know. I only have to evaluate the potential at very few points
(< 100) though, so this wont be too expensive.
What about the expansion coefficients - there must be a set for each
cell ?

Kristen

>
> --
> Anders
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