dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Wednesday 19 August 2009 14:57:20 Garth N. Wells wrote:
> 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

Precisely. 

After a second thought I think that doing it in the constructor is more clean. 
Makes life simpler. Is this also possible i UFL, I mean:

  e = FiniteElement("CG",cell,0,"facet")

Should it?

Johan

>      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
> >>>>
> >>>> _______________________________________________
> >>>> DOLFIN-dev mailing list
> >>>> DOLFIN-dev@xxxxxxxxxx
> >>>> http://www.fenics.org/mailman/listinfo/dolfin-dev
> >>>
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