dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Jan 18, 2007 at 12:03:14PM +0100, Johan Hoffman wrote:
> > On Thu, Jan 18, 2007 at 11:20:16AM +0100, Johan Hoffman wrote:
> >> Ok. I understand.
> >>
> >> So it is assumed that a discontinuous element is discontinuous along all
> >> cell faces.
> >
> > Yes.
> >
> >> Ideally you would like to be able to integrate over subdomains of the
> >> mesh; typically defined by the dx/ds-operators.
> >>
> >> Maybe something like:
> >>
> >> Mesh mesh("mesh.xml");
> >>
> >> Array<Face> surf_faces_1;
> >> surf_faces_1 = ...
> >>
> >> Array<Face> surf_faces_2;
> >> surf_faces_2 = ...
> >>
> >> mesh.defineSurface(surf_faces_1);
> >> mesh.defineSurface(surf_faces_2);
> >>
> >> [in form-file]
> >>
> >> ...
> >>
> >> a = (u,v)*ds1 + (u,v)*ds2
> >
> > Yes, that would be great, but there is no such support in the UFC
> > specification. It is always assumed that you integrate over the whole
> > mesh.
> >
> > So you need to define different forms for different meshes, but that
> > should be ok?
> 
> Maybe, as long as there is a natural way to add forms. If assembling
> matrices, I guess that you could always assemble different matrices for
> different meshes and then add them together in some way (although this
> appears a bit cumbersome?), and for adding the action of several forms I'm
> not sure what to do.
> 
> From my perspective I think the natural way would be to include the option
> of assembling over only a part of the mesh inside FFC/Dolfin::Assembler,
> rather than figuring out a way to add matrices/actions after assembly. As
> far as I can see, assembling over a submesh (volume or surface) should be
> as easy as using an bool-indicator MeshFunction over cells/faces inside
> the assembly loop.
> 
> What do you think?

Yes, you should be able to assembly over a subset of a mesh, but you
still need two forms. One form that you assembly on some subset of the
mesh and another form that you assemble over another subset.

/Anders