On 12/04/10 21:49, Anders Logg wrote:
On Mon, Apr 12, 2010 at 09:34:38PM +0800, Garth N. Wells wrote:
On 12/04/10 21:29, Anders Logg wrote:
On Mon, Apr 12, 2010 at 09:21:32PM +0800, Garth N. Wells wrote:
On 12/04/10 21:19, Garth N. Wells wrote:
On 12/04/10 20:47, Anders Logg wrote:
We are doing some work where we need to do run-time quadrature over
arbitrary polyhedra.
We (Mehdi and I) do this already (using UFC), so I don't see why a new
function is required. Can you explain why evaluate_tensor is not enough?
I meant 'tabulate_tensor'.
Which function do you call for evaluating the integrand?
We evaluate it inside ufc::tabulate_tensor. We construct our forms
with an extra argument, say an object "CutCellIntegrator", which can
provide quadrature schemes which depend on the considered cell.
That would require a special purpose code generator.
What's wrong with that? FFC won't (and shouldn't) be able to do
everything. Just adding a function to UFC won't make FFC do what we do
now. We reuse FFC (import modules) and add special purpose extensions.
Having
evaluate_integrand would allow more flexibility for users to implement
their own special quadrature scheme.
We make "CutCellIntegrator" an abstract base class, so the user has
*complete* freedom to define the quadrature scheme and the generated
code does not depend on the scheme, since the scheme may depend on
things like how the cell 'cut' is represented.
I also don't understand how it can work at all since the quadrature
points are not known at compile-time. Or do you a fixed set of reference
polyhedra that you map to?
The "CutCellIntegrator" object is asked for the quadrature points, and
it returns them. One way to do it is to sub-triangulate polyhedra (I
think that CGAL can do this). "CutCellIntegrator" would usually be aware
of intersecting surfaces, etc. It can also return schemes on surfaces.
I would like a quadrature generator on polyhedra to eventually be part
of DOLFIN.
Garth
--
Anders
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