dolfin team mailing list archive

[Kristian Oelgaard <k.b.oelgaard@xxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> On Thu, May 22, 2008 at 11:50:36AM +0200, Dag Lindbo wrote:
> > Anders Logg wrote:
> > > On Thu, May 22, 2008 at 11:26:41AM +0200, Dag Lindbo 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:   4224:c5a7da38ff2c966e5f2483b5232993fb75ac6aa1
> > >>> tag:         tip
> > >>> user:        Anders Logg <logg@xxxxxxxxx>
> > >>> date:        Thu May 22 10:19:48 2008 +0200
> > >>> files:       dolfin/fem/DirichletBC.cpp dolfin/fem/DirichletBC.h
> > >>> description:
> > >>> Major cleanup of DirichletBC:
> > >>>  - Store boundary facets in array, common for all different
> representations
> > >>>  - BCs may now be specified in 3 differenet ways: SubDomain,
> MeshFunction, or as Mesh data
> > >>>  - Should speed up repeated application of BCs
> > >>>  - Tested on a few different applications, but please check that
> nothing broke.
> > >>>    In particular, geometric and pointwise application has not been
> tested.
> > >> Noting broke here!
> > > 
> > > ok, nice. Thanks for checking (Kristian also).
> > > 
> > >> However, I'm not seeing the speedup... (and I'm reapplying the
> dirichlet
> > >> bcs every timestep). My code spends a good 30% of runtime applying
> > >> dirichlet BCs (linear systems are pre-factorized so the solve step
> takes
> > >> no time). Any hints?
> > > 
> > > The speedup may not be noticeable if a lot of time is spent on
> > > evaluating the function. Would be interesting to profile.
> > > 
> > > The difference from before is that each time apply() is called, we
> > > only iterate over the actual facets included in your subdomain of the
> > > boundary, not the entire mesh and then skipping those facets which
> > > don't belong to your boundary. Also, depending on which type of search
> > > ("topological", "geometric", "pointwise"), the new implementation
> > > should avoid initializing mesh facets.
> > > 
> > 
> > Does this mean that there now is a distinct difference in performance
> > between giving the subdomain as a class that inherits from SubDomain
> > (overloading bool inside) and pre-computing a mesh function with
> > subdomain markers? /Dag
> 
> There is some overhead but I don't know how big it is. The performance
> for the three different ways to specify boundary conditions should be
> 
>   MeshData > MeshFunction > SubDomain

Is there a demo somewhere that shows how to use MeshData and MeshFunction
instead of SubDomain?

Kristian
 
> For the three methods for finding dofs on facets, the performance
> should be
> 
>   topological > geometric > pointwise
> 
> -- 
> Anders
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