dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

Good to know it works.

PETSC_DECIDE would be nice, but I don't know how to implement it.

If anyone has a (simple) solution, I would be happy to add it.

/Anders


On Thu, Mar 23, 2006 at 02:05:28PM +0000, Alexander Jarosch wrote:
> Hi just tried out the new setup, works smoothly. thanks Anders, nice 
> work. May I add a comment. If you have time, it would be great to allow 
> also
> 
>   solver.set("Krylov shift nonzero", PETSC_DECIDE);
> 
> as well so that PETSc is deciding what to use, a nice feature, but as I 
> said only when time allows, definitely not a needed function.
> 
> /Alex
> 
> 
> 
> Anders Logg wrote:
> 
> >On Wed, Mar 22, 2006 at 10:17:10AM -0600, Anders Logg wrote:
> > 
> >
> >>On Wed, Mar 22, 2006 at 04:53:16PM +0100, Garth N. Wells wrote:
> >>   
> >>
> >>>On Wed, 2006-03-22 at 08:47 -0600, Anders Logg wrote:
> >>>     
> >>>
> >>>>On Wed, Mar 22, 2006 at 10:13:22AM +0000, Alexander Jarosch wrote:
> >>>>       
> >>>>
> >>>>>I got a bit lost in the current updates and now I just have a short 
> >>>>>question. I set up my solver like this:
> >>>>>
> >>>>>// Discretize equation
> >>>>>Matrix A;
> >>>>>Vector x, b;
> >>>>>FEM::assemble(*a, *L, A, b, mesh, bc);
> >>>>>
> >>>>>// Solve the linear system
> >>>>>KrylovSolver solver(Preconditioner::ilu);
> >>>>>KSP ksp;
> >>>>>ksp = solver.solver();
> >>>>>
> >>>>>PC pc;
> >>>>>KSPGetPC(ksp, &pc);
> >>>>>PCFactorSetShiftNonzero(pc, PETSC_DECIDE);
> >>>>>//PCFactorSetShiftPd(pc, PETSC_TRUE);
> >>>>>
> >>>>>solver.set("Krylov relative tolerance", 1e-14);
> >>>>>
> >>>>>solver.solve(A, x, b);
> >>>>>
> >>>>>but Petsc still complains about zero Pivot. should the line 
> >>>>>"PCFactorSetShiftNonzero(pc, PETSC_DECIDE);" not take care of that.
> >>>>>         
> >>>>>
> >>>>The problem is that KrylovSolver::solve() reads all parameters from
> >>>>the (DOLFIN) database, including "Krylov relative tolerance", and sets
> >>>>them before each solve. The solve() function also sets the
> >>>>preconditioner. Therefore, setting options manually by PETSc calls
> >>>>might not always work.
> >>>>
> >>>>The plan is to remove the KrylovSolver::solve() function if no one
> >>>>objects (Garth?). This will leave two options: either use the simple
> >>>>(but limited) DOLFIN wrapper or get the PETSc data structures and
> >>>>solve using PETSc calls:
> >>>>
> >>>>Mat Amat = A.mat();
> >>>>Vec xvec = x.vec();
> >>>>
> >>>>PETSc calls...
> >>>>
> >>>>       
> >>>>
> >>>Another option is to add PETSc options at the command line. This is
> >>>really easy,
> >>>
> >>> ./dolfin -pc_factor_shift_nonzero
> >>>
> >>>Just make sure that you have 
> >>> int main(int argc, char* argv[])
> >>>	
> >>>
> >>>     
> >>>
> >>>>That said, I will (re-)add a parameter for "Krylov shift nonzero" so
> >>>>you can do this natively in DOLFIN.
> >>>>
> >>>>I'll await comments from Garth and others before going ahead.
> >>>>
> >>>>/Anders
> >>>>
> >>>>       
> >>>>
> >>>I think that removing KrylovSolver.solver() is the best approach from a
> >>>robustness point of view. KrylovSolver then doesn't have to worry that a
> >>>user might have messed with the PETSc solver directly. I do find the
> >>>direct access to ksp useful, but I can live without.
> >>>
> >>>Garth  
> >>>     
> >>>
> >>ok, I'll make the update.
> >>
> >>/Anders
> >>   
> >>
> >
> >ok, I have added the new option. Try it and see if it works:
> >
> >   KrylovSolver solver(Preconditioner::ilu);
> >   solver.set("Krylov shift nonzero", whatever);
> >   solver.set("Krylov relative tolerance", 1e-14);
> >   solver.solve(A, x, b);
> >
> >/Anders
> >
> >_______________________________________________
> >DOLFIN-dev mailing list
> >DOLFIN-dev@xxxxxxxxxx
> >http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
> >
> > 
> >
> 
> 

-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/