dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Wednesday 19 August 2009 15:12:21 Garth N. Wells wrote:
> Johan Hake wrote:
> > 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?
>
> Is that a PyDOLFIN finite element? If it is, then yes, that's how it
> should work.
>
> Somewhat related, it's a bit annoying in PyDOLFIN that the code is
> recompiled when the mesh is changed. Can we avoid this? Should one then
> create a finite element and a dof map with which to initialise the
> Pythin FunctionSpace?

Should be fixed in a patch comming soon to ffc

Johan

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