dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/6/12 Anders Logg <logg@xxxxxxxxx>:
> On Tue, Jun 10, 2008 at 05:08:57PM +0200, Martin Sandve Alnæs wrote:
>> 2008/6/10 Anders Logg <logg@xxxxxxxxx>:
>> > On Tue, Jun 10, 2008 at 04:41:25PM +0200, Martin Sandve Alnæs wrote:
>> >> Maybe this design works?
>> >>
>> >> x is coordinates, c is cell info
>> >>
>> >> class Function
>> >> {
>> >>   virtual void eval(v, x, c) { eval(v, x); }
>> >>   virtual void eval(v, x) { dolfin_error("Missing implementation of eval."); }
>> >> };
>> >>
>> >> class A: Function
>> >> {
>> >>   void eval(v, x) { do_my_thing; }
>> >> };
>> >>
>> >> class B: Function
>> >> {
>> >>   void eval(v, x, c) { do_my_thing; }
>> >> };
>> >>
>> >> The assembler always call eval(v,x,c), the user overloads the one
>> >> he wants. There are already lots of redirecting back and forth in
>> >> the Function hierarchy, so the overhead shouldn't become larger.
>> >> If a user-function that depends on cell info is called in a context
>> >> without cell info, i.e. eval(v,x) is called, this triggers an error.
>> >>
>> >> Inheritance in Python is probably a problem here (SWIG issues).
>> >> Alternatively, name them eval(v,x) and eval_cell(v,x,c) or something
>> >> to solve that problem.
>> >
>> > Good, but it becomes a bit messy if we also want to include the other
>> > hidden arguments (see protected section of Function):
>> >
>> >  /// Access current facet normal (available during assembly for user-defined function)
>> >  Point normal() const;
>> >
>> >  /// Access current facet (available during assembly for user-defined functions)
>> >  int facet() const;
>>
>> We could pack all geometry data in one argument.
>> Or have a separate eval_facet which takes these arguments.
>
> I think we should have eval_facet. But how do we pack geometry in one
> argument in C++? We might want the cell, the subdomain, the current
> time, and possibly other things.

How? A class/struct. Which basically amounts to the same thing as
having multiple arguments.

Maybe a FacetCell which holds its parent cell, the normal, and facet number?

The current time doesn't vary during assembly, we can leave that to the user.
Same with subdomain and meshfunction data: the function can look up this
itself if it knows which cell it is currently being evaluated in.

--
Martin