On Jan 14, 2008 11:24 AM, Yujie <recrusader at gmail.com> wrote: > Dear Matt and Hong: > > Based what you said, it looks like a little difficult to evalute the matrix > in PETSc, especailly regarding a big dimension. However, when I select > iterative methods, how to select a suitable one based on some evaluation? > Could you give me some advice? thanks a lot.
If I knew how to choose a method, I would retire. Anyone who tells you that they can is outright lying. The only alternative is to try them all. That is why we built PETSc. Matt > Regards, > Yujie > > On 1/14/08, Hong Zhang <hzhang at mcs.anl.gov> wrote: > > > > If you want few selected eigen solutions of sparse matrix, > > you should use sparse eigen solver. Take a look at' > > slepc (http://www.grycap.upv.es/slepc/) > > or use slepc interface with arpack. > > > > Hong > > > > > > On Mon, 14 Jan 2008, Yujie wrote: > > > > > Thank you for your advice. > > > I have used -ksp_compute_eigenvalues_explicitly to get the eigen values. > > > However, it is very very > > > slow because the dimension of the matrix is about ten thousand. > > > > > > Yujie > > > > > > On 1/14/08, Matthew Knepley <knepley at gmail.com> wrote: > > >> > > >> You can use > > >> > > >> > > >> > http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeEigenvaluesExplicitly.html > > >> > > >> with and without a preconditioner. We have not coded the SVD > > >> counterpart, but you can use > > >> > > >> > > >> > http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeExplicitOperator.html > > >> > > >> and then call the LAPACK yourself. > > >> > > >> Matt > > >> > > >> On Jan 13, 2008 11:23 PM, Yujie <recrusader at gmail.com> wrote: > > >>> Hi, everyone > > >>> > > >>> I want to select iterative methods by observing the singular values > > >>> decompostion of the matrix. However, I don't know how to get all the > > >>> singular values of the matrix in PETSc. I know the command > > >>> "-ksp_monitor_singular_value" may get the max and min singular values > at > > >>> each iteration. How to get the singular values of the matrix I want to > > >>> solve? In addition, when I use the preconditioned iterative method, > how > > >> to > > >>> get the singular values of the preconditioned iterative operator? > > >>> > > >>> thanks a lot. > > >>> > > >>> Regards, > > >>> Yujie > > >>> > > >> > > >> > > >> > > >> -- > > >> 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 > > >> > > >> > > > > > > > > > -- 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
