On Fri, 11 Apr 2008, Jed Brown wrote:
> On Fri 2008-04-11 16:47, [EMAIL PROTECTED] wrote: >> I ran ex3 using the runtime flags and I got the following error message: > > You'll have to add something like > > KSPSetInitialGuessNonzero(ksp, PETSC_FALSE); > > before the solve if you want to use preonly. I was unaware that > libmesh sets this by default. Yes; we have a lot of application codes which use projected coarse mesh solutions as initial guesses for a refined mesh, previous time steps' solutions as initial guesses for the next time step, etc. > A prettier way to unset this parameter might be a nice thing for > libmesh to do. I think we're going to be taking a harder look at our solver interface abstractions in the next few months. Previously most of the main developers just used PETSc for real work and LASPACK as an easy-to-install serial fallback, and just using PETSc's command line options has been too easy for us to bother abstracting many of them out. But, Ben Kirk and Derek Gaston have just started adding support for Trilinos' solvers, which should mean we'll be more interested in package-independent configuration soon. > I'd be surprised if you actually take a performance hit when leaving > the solver as gmres (default) and just specifying '-pc_type lu'. It > will converge after one iteration. This is what I typically do as a last resort; you'll generally converge to any reasonable tolerance in one iteration and to 1e-14 or so in two. The extra work in the Krylov solver is trivial for a problem where you're already falling back on the most expensive "preconditioner" there is. --- Roy ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
