dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

On Thursday 08 May 2008, you wrote:
> It helps me to think about it this way.  Count the number of ds terms in
> your form file.  If you have n terms, then any facet marked with (n-1)
> or larger will *NOT* get assembled.  So if you have 3 exterior
> subdomains (ds0, ds1, ds2 in your form file), then  the relevant markers
> will be 0, 1, and 2, and any number 3 or greater will not have an
> integral associated with it and therefore will not get assembled.  So if
> I were you I might consider the following logic.
>
>   /// first, since there are no dS terms
>   int_facet_domains = 0;
>
>   /// set all exterior facets to some number greater than the number of
> ds terms
>   ext_facet_domains = 4;
>
>   /// loop over facets
>   for (FacetIterator facet(mesh); !facet.end(); ++facet) {
>
>     /// Check if we have an exterior facet
>     if ( facet->numEntities(mesh.topology().dim()) != 2 ) {
>       if (first non-zero neumann condition) ext_facet_domains(*facet) = 0;
>       if (second non-zero neumann condition) ext_facet_domains(*facet) = 1;
>     }
>   }
>
>
It makes sense...in this way we don't have to care with the zero neumann 
boundary.  

>   assemble(A,a,mesh, cell_domains, ext_facet_domains, int_facets_domains);
>
> Here I am assuming that you are imposing you Dirichlet BC strongly.  If
> not (if you have the Dirichlet BC defined in your form file) add another
> ext_facet_domains(*facet) in the above loop.

I'm imposing strongly.

> > If i want to use different markers for the interior facets then i should
> > considerer 2 different MeshFunctions   with the correct order.
> > 0..n-1 for interior
> > 0..n-1 for exterior
> > ??
>
> Yes.  Remember that there is a one-to-one correspondence with the domain
> number in the form file and the marker number in the MeshFunction.  If
> ds0 = Integral("exterior facet", 0), and ds1 = Integral("exterior
> facet", 1) then the facets on ds0 need to be marked with 0 in
> ext_facet_domains, and the facets on ds1 need to be marked with 1 in
> ext_facet_domains etc.
>
> > And again, if you don't use dS in your forms, the assembler will not take
> > into account the third meshfunction, so it could be whatever you want,
> > right?
>
> Yes, that's right.
>
> Hope this is helpful.
> Jake
>

It's Very Helpful!!!


-- 
Nuno David Lopes