dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Feb 09, 2009 at 11:58:28AM +0100, Kent Andre wrote:
> 
> Is it the code in DofMap that is not understandable ? 
> 
> The idea behind the code is that the dof_map provides a numbering
> of the unknowns ie. the global dofs are  D = [0, 1, .....N-1]. 
> In the restricted function space we need a corresponding numbering
> R = [0, 1, .... M-1] where M < N. 
> 
> The code in restriction is such that it runs through all dofs in the
> restricted mesh (as it is now by runing through the whole mesh except 
> for the ones marked by the meshfunction). I run through all the dofs
> and for each dof I check the dof in the global mesh, If I already have
> seen this dof I use the same dof_number as last time (stored in
> R[dofs[k]]). If the dof is new I update the dof_counter and add
> the new dof to R. By doing this I get a new dof_map where each 
> node is numbered in an increasing sequence. 
> 
> Check also the demo under dolfin/demo/function/restriction. You can eg. 
> probably begin by changing demo.
> 
> 
> Kent 

The demo looks a little unfinished. Could you move it to

  dolfin/demo/function/restriction/python/demo.py

then add the copyright headers etc like in the other demos, clean it
up a little, add a C++ version in the cpp directory (or a copy of the
README file from other demos where the C++ version is missing). You
can also move it to the sandbox until it's finished.

-- 
Anders


> 
> On ma., 2009-02-09 at 11:20 +0200, Evan Lezar wrote:
> > Kent
> > 
> > Thanks for the reply.  I have started to have a look at the code to
> > make the changes that you suggested, but must admit that I am a little
> > lost.
> > 
> > I will continue to work on it, but any other tips would be greatly
> > appreciated.
> > 
> > Thanks
> > Evan
> > 
> > On Wed, Feb 4, 2009 at 10:50 PM, <kent-and@xxxxxxxxx> wrote:
> >         
> >         Hi,
> >         
> >         Here are my rough thoughts on it.
> >         
> >         In FunctionSpace there is a function restriction which creates
> >         a
> >         (restricted) DofMap based
> >         on a mesh, a ufc:.dofmap and a MeshFunction. The way I have
> >         implemented,
> >         this function is such that the MeshFunction contains booleans
> >         that
> >         indicates which cells
> >         that should be used in the DofMap. It could equally well be
> >         vertices or other
> >         mesh entities, but the way restriction is implemented now, it
> >         has to be
> >         cells.
> >         It should however be relatively easy to change it to other
> >         entities (I
> >         think).
> >         Changing this would give a loc2glob array which contains -1
> >         for the entries
> >         that should not be used. As I understand, petsc will then
> >         avoid these entries
> >         so it might work, at least for petsc, with only this
> >         alteration in the
> >         function restriction.
> >         
> >         Kent
> >         
> >         
> >         > Hi
> >         >
> >         > Since I last rasied this issue there have been a lot of
> >         changes (great
> >         > ones
> >         > I must add) to the fenics codebase, so I thought I would ask
> >         again.
> >         >
> >         > I am interested in removing the rows and columns of the
> >         finite element
> >         > matrices (for vector electromagnetic problems) associated
> >         with zero valued
> >         > Dirichlet boundary conditions.  It is important that the
> >         original degrees
> >         > of
> >         > freedom (or a mapping between the two sets) be available so
> >         that the
> >         > solution of a system of equations or an eigenvalue problem
> >         can be used to
> >         > visualize the solution, for example.
> >         >
> >         > The removal of the degrees of freedom has two advantages
> >         that I can think
> >         > of
> >         > (for my applications at any rate).  The first is that the
> >         systems being
> >         > solved will be smaller.  The second is of particular concern
> >         to me as I am
> >         > often solving eigenvalue problems and the unity eigenvalues
> >         that are
> >         > introduce when applying the Dirichlet BCs in their current
> >         form
> >         > contaminate
> >         > the spectrum in many of my examples.
> >         >
> >         > Any thoughts or assistance would be greatly appreciated.
> >         >
> >         > Thanks
> >         > Evan
> >         
> >         > _______________________________________________
> >         > DOLFIN-dev mailing list
> >         > DOLFIN-dev@xxxxxxxxxx
> >         > http://www.fenics.org/mailman/listinfo/dolfin-dev
> >         >
> >         
> >         
> > 
> 
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