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.
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 > >> > >> > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20080114/b9dddfee/attachment.htm>
