dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Sep 11, 2008 at 03:02:36PM +0100, Garth N. Wells wrote:
> 
> 
> Anders Logg wrote:
> > On Thu, Sep 11, 2008 at 02:51:41PM +0100, Garth N. Wells wrote:
> >> Martin Sandve Alnæs wrote:
> >>> I don't agree, isn't the point that several DiscreteFunctions can
> >>> share a FunctionSpace?
> >>>
> >> Yes, but a dof map doesn't define a function space.
> >>
> >> Garth
> > 
> > I think the dof map should be in the FunctionSpace, that way several
> > functions may share the dof map (which may take time to compute if we
> > want to do some reordering).
> > 
> > Two functions in the same function space share the mesh, the element
> > and the dof map (these three define the space) but each function has
> > its own vector.
> > 
> 
> My point isn't that a DofMap won't shared, it's that it's not part of 
> the definition of a function space.

It is part of the function space if we say that a function space is
defined by a particular basis:

  V = span{\phi_i}

To define the basis, we need the dof map.

> It always possible that two discrete functions which are equivalent can 
> share a mesh and finite element (which defines the function space), but 
> have different vectors and dof maps.

Is that something we will encounter much? It would simplify matters if
we said that a FunctionSpace is a function space with a particular
basis. We do that anyway if we include the finite element. Otherwise,
we could say that (P_1)^d and BDM_1 are the same function space, but
we think of them as different.

> > I added the FiniteElement class to avoid exposing ufc:: classes
> > directly. We do the same for ufc::dof_map (but then we have a reason).
> > It might not be necessary, but it looked more uniform to have
> > 
> >   (Mesh, FiniteElement, DofMap)
> > 
> > instead of
> > 
> >   (Mesh, ufc::finite_element, DofMap)
> > 
> 
> Sure. I just can't find where FiniteElement is defined?
> 
> Garth

I thought I had pushed it. It should be pushed now.

-- 
Anders

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