dolfin team mailing list archive

[Marie Rognes <meg@xxxxxxxxx>]

Garth N. Wells wrote:
> Marie Rognes wrote:
> > Anders Logg wrote:
> > > On Fri, Oct 30, 2009 at 10:20:31AM +0000, Garth N. Wells wrote:
> > >  
> > > > Marie Rognes wrote:
> > > >    
> > > > > DOLFIN wrote:
> > > > >      
> > > > > > One or more new changesets pushed to the primary dolfin repository.
> > > > > > A short summary of the last three changesets is included below.
> > > > > >
> > > > > > changeset:   7408:f32a6ec49c47
> > > > > > tag:         tip
> > > > > > user:        Anders Logg <logg@xxxxxxxxx>
> > > > > > date:        Thu Oct 29 23:28:47 2009 +0100
> > > > > > files:       dolfin/fem/DofMap.cpp dolfin/fem/DofMap.h
> > > > > > dolfin/function/FunctionSpace.cpp dolfin/function/FunctionSpace.h
> > > > > > dolfin/mesh/Mesh.h
> > > > > > description:
> > > > > > First iteration of refinement of function spaces. Refinement of a
> > > > > > function
> > > > > > space should take care of refining the mesh, rebuilding the 
> > > > > > dofmap and
> > > > > > interpolating all its member functions to the new function space.
> > > > > >
> > > > > > All essential bits should be in place but needs some debugging to
> > > > > > find memory errors/leaks.
> > > > > >
> > > > > >
> > > > > >         
> > > > > This seems to be not working quite optimally yet.
> > > > >
> > > > > 1) The attached script fails with the error:
> > > > >
> > > > >
> > > > >    python: dolfin/function/Function.cpp:392: virtual void
> > > > >    dolfin::Function::compute_vertex_values(double*, const
> > > > >    dolfin::Mesh&) const: Assertion `&mesh == 
> > > > > &_function_space->mesh()'
> > > > >    failed.
> > > > >    Aborted
> > > > >
> > > > >
> > > > > 2) The original mesh does not seem to be refined. Shouldn't it be?
> > > > >
> > > > > 3) Not much seems to happen if f is an Expression (since not much 
> > > > > seems
> > > > > to happen with the mesh)
> > > > >
> > > > > 4) What happens when there are multiple function spaces associated 
> > > > > with
> > > > > one mesh?
> > > > >
> > > > >       
> > > > I haven't looked at the code yet, but my first reaction to the commit
> > > > log is related to the above two points. I wonder if it's wise to 
> > > > make a
> > > > FunctionSpace aware of the Functions that depend on it. It makes
> > > > FunctionSpace more complicated and things could get very tricky in
> > > > parallel. Also, there is some freedom in how a Function is moved from
> > > > one mesh to another.
> > > >
> > > > Would could define a new class, something like FunctionCollection (I
> > > > haven't given any thought to an appropriate name) which could collect
> > > > FunctionSpaces and GenericFunctions together for modification. It 
> > > > could
> > > > provide a default method for transferring a Function from one mesh to
> > > > another (say, interpolation), and a virtual interface for the user to
> > > > provide the transfer.
> > > >     
> > > That seems like a complication. It would introduce a new abstraction
> > > for what is essentially a function space.
> > >
> > > Perhaps the simplest and clearest option is the following:
> > >
> > > # Refine function space (W is a new space, not sharing any data)
> > > W = V.refine()
> > >
> > > # Transfer function from V to W
> > > w = project(v, W) # or
> > > w = interpolate(v, W)
> > >
> > >   
> >
> > I don't quite see the advantage of this approach:
> >
> > There is already existing mesh refinement functionality. A new 
> > function space can
> > be pretty easily constructed on a new (refined) mesh. But if a new 
> > function space
> > is created,  then any form defined on the previous space must 
> > probably be updated to
> > the new space. 
>
> Isn't this a good thing? One may not wish to update all forms to the 
> refined mesh.

Yes, that is probably a good thing :)

> > In particular, all basis functions either have to be
> > reinitialized (or somehow updated) and all the functions projected.
> >
> > This can a bit of a pain.
>
> This is why I thought it would be useful to have a structure which 
> holds the forms and functions which one would like to update. It could 
> take care of updating/projecting collections of forms and functions.

Something like:

   mesh = ...
   form = ... something on old mesh ...

   new_mesh = mesh.refine()
   new_form = update(form, new_mesh)


?

--
Marie


> Garth
>
> > I don't see the purpose of modifying the mesh-refinement-apparatus 
> > unless the
> > modification actually alleviates a bit of that pain.
> >
> > --
> > Marie
> >
> >
> >
> >
> >
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