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Re: [FFC-dev] [HG FFC] Restrictions appears to be working for the Poisson demo.

 



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

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