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, <[email protected]> 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 > > > [email protected] > > > http://www.fenics.org/mailman/listinfo/dolfin-dev > > > > > > > > > > > _______________________________________________ > DOLFIN-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/dolfin-dev
signature.asc
Description: Digital signature
_______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
