On Tue, Sep 15, 2009 at 8:29 PM, Matthew Knepley <knepley at gmail.com> wrote:
> On Tue, Sep 15, 2009 at 6:04 PM, Ryan Yan <vyan2000 at gmail.com> wrote: > >> Thanks Jed. >> >> And in the term ||Ae||/||Ax||, PETSc impilictly assume that we use zero >> as initial guess and here the x really means exact solution, right? >> > > This has nothing to do with the initial guess. Ae is the residual, and x is > the current guess. We do not have the exact solution, > but I guess A x^* = b, so that could have been used. > > Thanks Matt. I agree that in the print out ||Ae||/||Ax||, x here just represents the x*. Yan > Matt > > >> >> Yan >> >> >> >> >> On Tue, Sep 15, 2009 at 6:41 PM, Jed Brown <jed at 59a2.org> wrote: >> >>> Ryan Yan wrote: >>> > But can you say a little more about what happened in the first >>> scenario, I >>> > did not quite fellow you. Let's say, If I set -ksp_rtol 1e-2, what does >>> this >>> > mean in the left PC case. More specifically, which term will be >>> considered >>> > as a stop creteria for the KSP solve. >>> >>> Look at the first column (preconditioned residual norm). Notice that >>> this is decreasing by 1e-2 and 1e-3 respectively in your examples. >>> >>> Jed >>> >>> >> > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090915/6e99f6a1/attachment.htm>