[firedrake] Specify boundary conditions at a corner

[Lawrence Mitchell]

> On 28 Aug 2015, at 00:38, Justin Chang <jychang48 at gmail.com> wrote:
> 
> So if I use a GMSH file, the third argument in DirichletBC(...) would
> correspond to whatever the Physical IDS are? Would it correspond to
> "Face set" values if I were to use an exodusii file?

Yes, that's right. This is meant to work, but I think we have tested the exodus reader less extensively than the gmsh one, so please do complain if things don't work. 

Cheers,

Lawrence