dolfin team mailing list archive

[Evan Lezar <evanlezar@xxxxxxxxx>]

On Mon, Feb 9, 2009 at 1:05 PM, Anders Logg <logg@xxxxxxxxx> wrote:

> 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
>
>
Regarding the demo.

I have just tried to run it, and it fails with Petsc reporting a
Segmentation Violation.

Evan


>
> >
> > 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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