dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Apr 24, 2007 at 05:28:46PM +0200, Garth N. Wells wrote:
> 
> 
> Anders Logg wrote:
> > On Tue, Apr 24, 2007 at 04:37:13PM +0200, Garth N. Wells wrote:
> >> I've done some rough timings for assembly of the elasticity demo with 
> >> the mesh refined once. For assembly, things are much faster (almost a 
> >> factor 3), but the application of Dirichlet boundary conditions has 
> >> become very expensive. Both the creation of sub-domains and the 
> >> application of the boundary conditions appears to be quite costly. Of 
> >> the time required for mesh initialisation, refinement, assembly and 
> >> application of boundary conditions, more the 50% of the runtime involves 
> >> the application of the boundary conditions. In version 0.64, the 
> >> application of boundary conditions involves almost zero overhead.
> >>
> >> Garth
> > 
> > Strange... There are are a few differences in how the bcs are handled
> > compared to 0.6.4 but I didn't think these would introduce any
> > overhead. Here are the major differences:
> > 
> > 1. We loop over the whole domain, not just the boundary
> > 
> > This means we can set Dirichlet conditions in the interior as well as
> > on the boundary. The overhead should be small, since before we always
> > created a BoundaryMesh before iterating over the boundary and that
> > creation involves an iteration over the entire mesh, as well as
> > creating the new data for the boundary mesh. 
> > 
> > 2. We create the mesh functions for the sub domains
> > 
> > This is only done when a mesh function has not been supplied. If you
> > have a mesh function that specifies the sub domains, then this step is
> > not needed. Perhaps we could do some optimization in the
> > BoundaryCondition constructor.
> > 
> 
> Creating the sub-domains is very expensive: 11.1 / 24 s. Application of 
> the boundary conditions (bc.apply(. . .)) requires 3.41 / 24 s, which 
> still seems like quite a lot.
> 
> Garth

ok, so we need to look into that. I'm working on getting the Stokes
demo working (setting bcs for sub systems) but I can take a closer
look when I'm done (if you don't find a solution before then).

Creating the sub domains should be just as expensive as creating the
BoundaryMesh in the old code.

/Anders