dolfin team mailing list archive

[Matthew Knepley <knepley@xxxxxxxxx>]

On Sun, Apr 5, 2009 at 2:54 PM, Anders Logg <logg@xxxxxxxxx> wrote:

> Dirichlet BC would need to be added in/after each multiplication and
> it should be possible to build it into the mult() operator and make it
> efficient.


I still think the best way to handle this is to eliminate them, as I talked
about
last time at Simula.

  Matt


>
> We can add a class to handle this after the release. Any suggestions
> for a good name? ActionMatrix? Action? ActionKrylovMatrix?
>
> --
> Anders
>
>
> On Sun, Apr 05, 2009 at 08:31:58AM -0500, Robert Kirby wrote:
> > Anders, Martin:
> > Dirichlet Boundary conditions?
> >
> >
> > On Sun, Apr 5, 2009 at 5:58 AM, Martin Sandve Aln s <martinal@xxxxxxxxx>
> wrote:
> >
> >     UFL defines action so you don't have to rewrite/duplicate your form:
> >
> >     a = u*v*dx
> >     b = action(a, f) # == f*v*dx
> >
> >     Martin
> >
> >
> >
> >     On Sun, Apr 5, 2009 at 10:34 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> >     > On Sat, Apr 04, 2009 at 08:30:39PM -0500, Robert Kirby wrote:
> >     >> Thanks, I'll take a look next week.
> >     >>
> >     >> One thought that would take a little work but might be worth
> exploring
> >     from the
> >     >> ffc end would be
> >     >> to define matrix actions in the form compiler that map to
> KrylovMatrix
> >     rather
> >     >> than Matrix.
> >     >> For example, one can take the Poisson code, replacing the
> TrialFunction
> >     with
> >     >> Function, so that
> >     >>
> >     >> v = TestFunction(V)
> >     >> u = Function(V)
> >     >> a = dot(grad(v), grad(u))*dx
> >     >>
> >     >> and then generate code for a KrylovMatrix subclass.  Anders and I
> >     experimented
> >     >> with the effects of ferari-optimization and found that they were
> most
> >     profound
> >     >> in this context.  It also removes the assembly bottleneck since
> you
> >     don't have
> >     >> to beat on a sparse matrix.  On the other hand, you don't have the
> >     matrix to
> >     >> feed to algebraic preconditioners.  No free lunch.
> >     >>
> >     >> Rob
> >     >
> >     > This wouldn't require anything on the FFC end. It would just
> require a
> >     > new C++ class which subclasses either of the Krylov matrices (or
> maybe
> >     > a new GenericKrylovMatrix) that takes a linear form (like your 'a'
> >     > above) to the constructor and calls assemble() in the overloaded
> mult().
> >     >
> >     > This should be easy to add.
> >     >
> >     >
> >     >
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