dolfin team mailing list archive

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

Johan Hake wrote:
> 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.
>
> I meant UFL.FiniteElement.

OK. I don't know if that is the syntax. Kristian will know.

> > 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?
>
> Do you mean when one has refined a mesh? 

Yes, or just changed from one simulation to the next.

As far as I understand it is the
> reason for this that we need to recompute the dofmap. 

In C++ we create a dolfin::FunctionSpace from a dolfin::FiniteElement, a 
dolfin::DofMap and a dolfin::Mesh. The FiniteElement and DofMap are 
created with a ufc::finite_element and a ufc::dof_map, respectively.

In the Python interface, in addition to what we have now, we would need 
FiniteElement and DofMap objects, with which we could create a 
FunctionSpace (together with a Mesh). Then, hopefully we could avoid 
recompilation when just the mesh is changed.

Garth

> How is this done in the C++ interface. 
>
> 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
> > > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > DOLFIN-dev mailing list
> > > > > > > > DOLFIN-dev@xxxxxxxxxx
> > > > > > > > http://www.fenics.org/mailman/listinfo/dolfin-dev
> > > > > > > ---------------------------------------------------------------------
> > > > > > > -- -
> > > > > > >
> > > > > > > _______________________________________________
> > > > > > > DOLFIN-dev mailing list
> > > > > > > DOLFIN-dev@xxxxxxxxxx
> > > > > > > http://www.fenics.org/mailman/listinfo/dolfin-dev
> > > > > > _______________________________________________
> > > > > > DOLFIN-dev mailing list
> > > > > > DOLFIN-dev@xxxxxxxxxx
> > > > > > http://www.fenics.org/mailman/listinfo/dolfin-dev