On Thu, Jul 03, 2008 at 06:07:08PM +0100, Garth N. Wells wrote:
Kent-Andre Mardal wrote:
On to., 2008-07-03 at 08:03 +0100, Garth N. Wells 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: 4374:6e1db926186ebfe9d9316b729a7d5747be3c5115
tag: tip
parent: 4373:8f4accd9eb039d0d13412e8d871e7f1bfce896b8
parent: 4372:3abbccc877d3bb358c76ef36dbbe252155b88183
user: Kent-Andre Mardal <kent-and@xxxxxxxxx>
date: Wed Jul 02 16:02:17 2008 +0200
files: dolfin/fem/Assembler.cpp dolfin/fem/DirichletBC.cpp site-packages/dolfin/assemble.py
description:
merge
changeset: 4373:8f4accd9eb039d0d13412e8d871e7f1bfce896b8
parent: 4369:b272b94b43ae789e2c72c90f6a027ce9fb89f6fc
user: Kent-Andre Mardal <kent-and@xxxxxxxxx>
date: Wed Jul 02 16:01:09 2008 +0200
files: demo/pde/sym-dirichlet-bc/demo.py dolfin/fem/Assembler.cpp dolfin/fem/Assembler.h dolfin/fem/DirichletBC.cpp dolfin/fem/DirichletBC.h dolfin/fem/assemble.cpp dolfin/fem/assemble.h dolfin/la/AssemblyMatrix.cpp dolfin/la/AssemblyMatrix.h dolfin/la/EpetraMatrix.cpp dolfin/la/EpetraMatrix.h dolfin/la/EpetraVector.cpp dolfin/la/EpetraVector.h dolfin/la/GenericMatrix.h dolfin/la/GenericTensor.h dolfin/la/GenericVector.h dolfin/la/Matrix.h dolfin/la/PETScMatrix.cpp dolfin/la/PETScMatrix.h dolfin/la/PETScVector.cpp dolfin/la/PETScVector.h dolfin/la/Scalar.h dolfin/la/Vector.h dolfin/la/uBlasMatrix.h dolfin/la/uBlasVector.cpp dolfin/la/uBlasVector.h dolfin/swig/dolfin_fem_pre.i dolfin/swig/dolfin_headers.i site-packages/dolfin/assemble.py
description:
implemented symmetric handling of boundary conditions
Great.
I looked at the demo but could see how to specify the method for
applying boundary conditions. Could you write a short description on how
to use it and it compares in terms of performance?
Garth
Can you explain to me what the different methods do ? I assume you refer
to the topological, geometric, pointwise switch in computeBC (which
is used).
I haven't looked at it in detail for some time, so I have to defer to
Anders and Kristian for a good explanation.
We have implemented 3 different strategies for locating the dofs for
which strong boundary conditions should be enforced:
1. Topological search
This will iterate over all boundary facets, and for each facet
tabulate the dofs that are on the facet using the UFC function
tabulate_facet_dofs. The BCs will be enforced for all these dofs.
This means that BCs will be enforced for all dofs belonging to a facet
which is *entirely on the boundary*. As a consequence, BCs will not be
enforced for dofs that happen to lie on the boundary but which belong
to a facet which is not on the boundary.
For example, BCs will not be enforced for some vertex dofs that are on
the boundary. This does not matter for continuous elements, since a
vertex dof will belong to at least one facet which is on the boundary
(even if it also belongs to another facet which is not on the
boundary). However, for DG methods this does matter.
2. Geometric search
This will iterate over all boundary facets and locate all nearby dofs
which are on the facet, using the UFC function tabulate_coordinates
and test the location of the dofs geometrically against the location of
the facet. This is slower than the topological search, but catches
the dofs that the topological search may miss.
3. Pointwise
This will iterate over all cells (not only the boundary facets) of the
entire mesh and call the inside() function of a SubDomain to check
which dofs should be constrained. This allows setting boundary
conditions pointwise (even inside the domain).
------------------------------------------------------------------------
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