dolfin team mailing list archive

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

On Tue, 2006-07-04 at 11:32 +0200, Garth N. Wells wrote:
> On Tue, 2006-07-04 at 11:24 +0200, Anders Logg wrote:
> > On Tue, Jul 04, 2006 at 09:12:48AM +0200, Anders Logg wrote:
> > > I'm wondering about how to specify the interface for uBlas
> > > preconditioners. I think the natural would be
> > > 
> > >     void solve(DenseVector& x, const DenseVector& b);
> > > 
> > > but it seems that the Krylov solver prefers an in-place
> > > 
> > >     void solve(DenseVector& x);
> > > 
> > > where x = b before the call.
> > > 
> > > I think we need to have just one interface. There are two
> > > options. Either we force the solve(x, b) interface, which I think
> > > we can do without sacrificing performance, or we force the solve(x)
> > > interface, which might not be natural for all types of
> > > preconditioners.
> > > 
> > > A Jacobi preconditioner would need to store a separate vector and make
> > > an additional copy which seems unnessary.
> > > 
> > > /Anders
> > > _______________________________________________
> > > DOLFIN-dev mailing list
> > > DOLFIN-dev@xxxxxxxxxx
> > > http://www.fenics.org/mailman/listinfo/dolfin-dev
> > 
> > I have modified the uBlas preconditioning interface and moved the ILU
> > preconditioner to a separate class. Here are the timings for the
> > benchmark, before and after the change:
> > 
> > Before change
> > -------------
> > 
> > Solving linear system of size 38809 x 38809 (Krylov solver).
> > Krylov solver (gmres, ilu) converged in 2851 iterations.
> > norm(x) 12.2
> > PETSc Krylov solve time = 33.2
> > uBlas assembly time = 0.29
> > Solving linear system of size 38809 x 38809 (uBlas Krylov solver).
> > Krylov solver converged in 2771 iterations.
> > norm(x) 12.2
> > uBlas Krylov solve time = 26.7
> > Factor ( < 1 mean uBlas is faster ) 0.805
> > 
> > After change
> > ------------
> > 
> > Solving linear system of size 38809 x 38809 (Krylov solver).
> > Krylov solver (gmres, ilu) converged in 2851 iterations.
> > norm(x) 12.2
> > PETSc Krylov solve time = 33.2
> > uBlas assembly time = 0.3
> > Solving linear system of size 38809 x 38809 (uBlas Krylov solver).
> > Krylov solver converged in 2744 iterations.
> > norm(x) 12.2
> > uBlas Krylov solve time = 27
> > Factor ( < 1 mean uBlas is faster ) 0.814
> > 
> > Some more work (a few extra copies) is made so it might be marginally
> > slower than yesterday (26.7 --> 27.0, about 1%).
> > 
> > Here's the new interface for solving with GMRES and ILU
> > preconditioning:
> > 
> >   uBlasKrylovSolver solver(uBlasKrylovSolver::gmres);
> >   uBlasILUPreconditioner pc(A);
> >   solver.solve(A, x, b, pc);
> > 
> > Garth, take a look and see if you like it. I'll keep my hands of the
> > linear algebra now for a while so if you want to do the templating and
> > renaming of the matrix/vector classes, please go ahead.
> > 
> 
> Looks fine.
> 
> Garth.
> 

One thing - wouldn't it be better if the Krylov solver is preconditioned
by default?

Garth

> > It should now be "easy" to move the ODE solvers from PETSc to uBlas.
> > 
> > /Anders
> > _______________________________________________
> > DOLFIN-dev mailing list
> > DOLFIN-dev@xxxxxxxxxx
> > http://www.fenics.org/mailman/listinfo/dolfin-dev
> 
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