dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Sep 25, 2008 at 03:11:27PM +0100, Garth N. Wells wrote:
> 
> 
> Anders Logg wrote:
> > On Thu, Sep 25, 2008 at 12:41:33PM +0100, Garth N. Wells wrote:
> >> Nuno David Lopes wrote:
> >>> Is there a simple way of setting an initial guess for an Iterative 
> >>> LinearSolver? 
> >>> In Umfpack and PETSc the default initial guess is the zero vector right?
> >> At the moment, yes (note the UMFPACK is an LU solver, so an initial 
> >> guess doesn't do anything).
> >>
> >> It's very simple, and I've been meaning to add an option for using an 
> >> initial guess. It's also useful for Newton solvers. I'll add something 
> >> in the next few days.
> >>
> >> Garth
> > 
> > It would be natural to let the x argument always be the initial
> > guess. I thought we already did this.
> > 
> > Would it be enough to make sure that Vector::init() does not reset the
> > values to zero?
> > 
> 
> Yes.
> 
> The danger is if someone sends an uninitialised vector to the solver.
> 
> Garth

We can just put something like this in the init() functions:

  if (x && size() == N)
    return;

I think we had this a while back but at some point VecZeroEntries was
inserted.

-- 
Anders

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