dolfin team mailing list archive

["Andy Ray Terrel" <aterrel@xxxxxxxxxxxx>]

I would look at dolfin/demo/pde/poisson.  I am usually able to provide a
user defined function that accomplishes this.
Andy

On Wed, May 7, 2008 at 10:19 AM, Nuno David Lopes <ndl@xxxxxxxxxxxxxx>
wrote:

> Are there any demos of Neumann boundary conditions implementation as in
> dolfin-manual:
> "It is also possible to define g only on 1 and specify an integral over
> the boundary subset 1 in the form file."  ???
>
> Can't find anything  about subdomains treatment in ffc form files vs
> assembling in dolfin cpp file.
>
> Thanks in advance!
>
>
> On Wednesday 07 May 2008, Nuno David Lopes wrote:
> > >You can define a form as a sum of contributions from different
> > >subdomains, for example:
> > >
> > >dx0 = Integral("cell", 0)
> > >dx1 = Integral("cell", 1)
> > >
> > >a = v*u*dx0 + dot(grad(v), grad(u))*dx1
> > >
> > >This gives two terms, one of which will be used in subdomain 0 and the
> > >other in subdomain 1.
> > >
> > >Subdomains can be specified in DOLFIN by creating a subclass of
> > >SubDomain and overloading the inside() function, or by specifying a
> > >MeshFunction<uint> over the cells of the mesh.
> > >
> > >You can also have integrals over arbitrary facets of the domain, like
> > >for example the boundary between your two subdomains. You can have
> > >several such integrals:
> > >
> > >  ds0 = Integral("exterior facet", 0)
> > > ds1 = Integral("exterior facet", 1)
> > >  ds2 = Integral("exterior facet", 2)
> > >
> > >  dS0 = Integral("interior facet", 0)
> > > dS1 = Integral("interior facet", 1)
> > >  dS2 = Integral("interior facet", 2)
> > >
> > >--
> > >Anders
> >
> > But how could we link the subdomains markers defined in a MeshFunction
> > with the variational form in the cpp.
> > Example:
> >
> > I have in a "Foo.form"  something like:
> > -------------------------------------------------------------------
> > P1=FiniteElement("Lagrange","tetrahedron",1)
> >
> > f=Function(P1)
> >
> > dx0 = Integral("cell", 0)
> > dx1 = Integral("cell", 1)
> >
> > a = f*v*u*dx0 + dot(grad(v), grad(u))*dx1
> > ------------------------------------------------------------------
> > and in "main.cpp" something like
> >
> ---------------------------------------------------------------------------
> >------------------------------- MeshFunction<unsigned int>
> > b_subdomains(mesh,"b_subdomains.xml");
> > //Boundary subdomain markers
> >
> > MeshFunction<unsigned int> v_subdomains(mesh,"v_subdomains.xml");
> > //Volume subdomain   (0 and 1) markers
> >
> > Function f(mesh,10.0);
> > FooBilinearForm a( f );//constructors for finite element form's (Problem
> > here)
> >
> ---------------------------------------------------------------------------
> >-------------------------------- I'm missing something...
> >
> > Shouldn't
> > FooBilinearForm a( f );
> > be replaced by  something like
> > FooBilinearForm a( f ,v_subdomains);  ?
>
>
> --
> Nuno David Lopes
>
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