ffc team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Johan Hake wrote:
> On Wednesday 19 August 2009 14:21:12 Garth N. Wells wrote:
> > Garth N. Wells wrote:
> > > Kent Andre wrote:
> > > > > Not sure what we have to do actually. I suppose I want get any clue
> > > > > from the
> > > > >   demo/function/restriction
> > > > >
> > > > > demo?
> > > > > I see that Kent has modified the dolfin.FunctionSpace to reflect the
> > > > > present (broken) implementation of restriction, anything in that
> > > > > line? Should such an implementation has been done in
> > > > > FunctionSpaceBase instead of FunctionSpace? Kent?
> > > > >
> > > > > Johan
> > > > This restriction is different in the sense that the restriction is made
> > > > by the standard element on a sub mesh.
> > > > The restriction in focus now is on the complete mesh but for only
> > > > a part of the element.
> > > > Combined, these two features will be very powerful.  I guess the
> > > > sub-mesh restriction stuff is broken due to the parallel mesh.
> > > I've attached an example solver. To make it work for P^k with k > 2 we
> > > need to restrict some functions to cell facets. Using FFC, we do
> > >
> > >     scalar  = FiniteElement("Lagrange", "triangle", 3)
> > >     dscalar = FiniteElement("Discontinuous Lagrange", "triangle", 3)
> > >
> > >     # This syntax restricts the space 'scalar' to cell facets.
> > >     mixed = scalar["facet"] + dscalar
> > >
> > > In PyDOLFIN we could do
> > >
> > >     V_dg = FunctionSpace(mesh, "DG", 3)
> > >     V_cg = FunctionSpace(mesh, "CG", 3, "facet")
> > >
> > >     mixed = V_cg + V_dg
> > I see now that we need to have the above option since the everything
> > (e.g. the dof map) is created and compiled inside functionspace.py.
>
> We could implement it in FunctionSpaceBase, as an operator, returning a new 
> FunctionSpaceBase, with the restricted element as arguemnt.
>
> However my concerns go to a sub space of a restricted mixed space (if such 
> exists) see the other email. 
>
> If we go for 1, (as you have already done ;) ), we cannot create a restricted 
> mixed space using the addition syntax.
>
>   mixed = V1 + V2

Do you mean to then restrict mixed? I'm already doing

    V0 = FunctionSpace(mesh, "CG", 3, "facet")
    V1 = FunctionSpace(mesh, "DG", 3)

    mixed = V0 + V1

and it works. This type of restriction (we'll need to sort out our 
terminology) impacts the dofmap, which I why I think it needs to be 
involved in the creation of the function space.

Garth


> If we want a restricted mixed space we need to use the constructor.
>
>   mixed = MixedFunctionSpace((V1,V2),restriction="facet")
>
> Johan
>
> > Garth
> >
> > > or
> > >
> > >     V_dg = FunctionSpace(mesh, "DG", 3)
> > >     V_cg = FunctionSpace(mesh, "CG", 3)
> > >
> > >     mixed = V_cg["scalar"] + V_dg
> > >
> > > Garth
> > >
> > > > Kent
> > > >
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