dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> I'm not very familiar with the Newton solvers in PETSc.
> 
> If the speedup is only 10% and you have to sacrifice a lot of
> flexibility, maybe we may as well do it ourselves. In particular since
> your hand-coded Newton is about 20 lines of code and just the wrapper
> code for calling the PETSc Newton solver is much longer.

This is my feeling too. The PETSc solver requires a number of pointers to
functions to be passed around, rather than just passing objects, which makes
things more complex. Also, using our own Newton solver would allow settings for
the linear solver to be set through the usual DOLFIN linear solver class,
avoiding duplication in the nonlinear solver.

Garth

> 
> /Anders
> 
> 
> On Fri, Dec 02, 2005 at 05:14:11PM +0100, dolfin@xxxxxxxxxx wrote:
> > Commit from garth (2005-12-02 17:14 CET)
> > -----------------
> > 
> > Updates to nls demos.
> > 
> > The nonlinear solver demos solve using both the class NonlinearSolver
> (which exploits the PETSc Newton solvers) and a hand programmed Newton
> procedure. The PETSc solvers are typically about 10% faster for the tests
> I've done. However, the NonlinearSolver class and the interface to it would
> be simpler if I programmed the NewtonSolver, and just relied on the existing
> linear algerbra wrappers for PETSc vectors, matrices and linear solvers. I
> think that this would be better given that the speed-up using the PETSc
> solver is not so large, we could probably equal it with some with some
> optimisations. Also, we then restrict PETSc to the linear algerbra classes,
> limiting the intrusion of PETSc into DOLFIN. Are there reasons to stick with
> the PETSc Newton solvers that I might be missing?
> > 
> > Garth
> > 
> >   dolfin  src/demo/nls/nonlinearpoisson/main.cpp  1.2
> >   dolfin  src/demo/nls/poisson/main.cpp           1.2
> > 
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> > 
> 
> -- 
> Anders Logg
> Research Assistant Professor
> Toyota Technological Institute at Chicago
> http://www.tti-c.org/logg/
> 
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