Yujie, > > 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.
What do you mean "how to select a suitable one based on some evaluation?" Usually, one wants a few eigenvalues with largest or smallest magnitude, or eigenvalues in a real interval when matrix is Hermitian. Please refer slepc user manual, which gives detailed description. Hong > > 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 >>>> >>>> >>> >> >> >
