dolfin team mailing list archive

[jhoffman@xxxxxxxxxxx]

> On Fri, Jul 08, 2005 at 08:49:22AM +0200, jhoffman@xxxxxxxxxxx wrote:
>> > On Thu, Jul 07, 2005 at 08:11:00PM +0200, jhoffman@xxxxxxxxxxx wrote:
>> >> >> I agree that we should support both, although 2 would be the only
>> one
>> >> >> avoiding checking (for Karin & Johan) as far as I understand.
>> >> >
>> >> > It depends on what the user wants. If someone calls
>> >> >
>> >> >    FEM::applyBC(..., mesh, ...)
>> >> >
>> >> > then we have to iterate over the entire boundary. On the other
>> hand,
>> >> > if someone calls
>> >> >
>> >> >    FEM::applyBC(..., boundary, ...)
>> >> >
>> >> > then we only have to loop over that portion of the boundary.
>> >>
>> >> Yes, but doesn't this involve checking if we are on the "boundary" by
>> >> comparing boundary ID's?
>> >
>> > Only when generating the boundary. The implementation of the first
>> > function will look like
>> >
>> >     void applyBC(..., mesh, ...)
>> >     {
>> >         Boundary boundary(mesh);
>> >         applyBC(..., boundary, ...);
>> >     }
>> >
>> > When a boundary is generated, we have to iterate over the entire mesh
>> > and detect which entities are on the boundary. (This is automatically
>> > detected by the algorithms in BoundaryInit.)
>> >
>> > But when we iterate over entities (like edges) on a Boundary, then we
>> > really just iterate over the entities on the Boundary (not iterating
>> > over the entire mesh and skipping the interior).
>> >
>> > Also note that if we assemble more than once, then the boundary has to
>> > be computed only the first time (this is automatically handled by the
>> > Mesh class, it knows if the boundary has already been computed).
>> >
>> > /Anders
>>
>> Ok. You mean that the only case when the first function is used is when
>> one is only interested in the whole boundary of the domain, in which
>> case
>> this is stored in the Mesh class after being computed once. That makes
>> sense.
>
> Yep. :-)
>
>> And for the general case of the second function, one creates several
>> Boundary objects for each boundary condition to be applied.
>
> Yes, that sounds like a good idea; creating several Boundary objects
> with corresponding BoundaryCondition objects and calling applyBC() on
> each pair.
>
> The question is then if the BoundarySpecification class should just
> return true or false, not an integer, since one would also create
> multiple BoundarySpecification objects, one for each part of the
> boundary.
>
> /Anders

Yes, this is how I see it. This is what made me confused by the
BoundarySpecification implementation.

/Johan

>
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