http://www.mcs.anl.gov/petsc/documentation/faq.html#kspdiverged
On Jul 21, 2012, at 4:30 AM, Bao Kai wrote: > > HI, all, > > I am still suffering from the slow convergence rate of the KSP solution. > > I changed the code to use Petsc3.3 and then try the gamg precoditioner, the > convergence rate is better, while it took more total time because it took > much more time for each iteration and some extra time for pre-processing. > > I am wondering if there are some ways that can help me to investigate the > slow convergence rate for KSP solution so that I can do some improvement. Is > DMMG will be a good solution? > > Thank you very much. > > Best Regards, > Kai > > Message: 2 > Date: Wed, 11 Jul 2012 15:17:15 -0500 > From: Matthew Knepley <knepley at gmail.com> > To: PETSc users list <petsc-users at mcs.anl.gov> > Subject: Re: [petsc-users] Does this mean the matrix is > ill-conditioned? > Message-ID: > <CAMYG4Gk7T=q+w1PKO7G_TW07iDzux90Sncbv9K7d0FD-MDrLRg at > mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > On Wed, Jul 11, 2012 at 12:40 PM, Bao Kai <paeanball at gmail.com> wrote: > > > Hi, all, > > > > The following is the output from the solution of a Poisson equation > > from Darcy's law. > > > > To compute the condition number of matrix, I did not use PC and use > > GMRES KSP to do the test. > > > > It seems like that the condition number keep increasing during the > > iterative solution. Does this mean the matrix is ill-conditioned? > > > > Generally yes. Krylov methods take a long time to resolve the smallest > eigenvalues, so this approximation is not great. > > > > For this test, it did not achieve convergence with 10000 iterations. > > > > When I use BJOCABI PC and BICGSTAB KSP, it generally takes about 600 > > times iteration to get the iteration convergent. > > > > Any suggestion for improving the convergence rate will be much > > appreciated. The solution of this equation has been the bottleneck of > > my code, it takes more than 90% of the total time. > > > > Try ML or GAMG. > > Matt > > > > Thank you very much. > > > > Best Regards, > > Kai > > > >
