<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br class="webkit-block-placeholder"></div> You cannot compute all the eigenvalues for a large sparse matrix with PETSc alone.<div><br class="webkit-block-placeholder"></div><div> Barry</div><div><br><div><div>On Jan 14, 2008, at 11:24 AM, Yujie wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Dear Matt and Hong:<br><br>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. <br><br>Regards,<br>Yujie<br><br><div><span class="gmail_quote">On 1/14/08, <b class="gmail_sendername">Hong Zhang</b> <<a href="mailto:hzhang@mcs.anl.gov">hzhang@mcs.anl.gov</a>> wrote:</span><blockquote class="gmail_quote" style="margin-top: 0; margin-right: 0; margin-bottom: 0; margin-left: 0; margin-left: 0.80ex; border-left-color: #cccccc; border-left-width: 1px; border-left-style: solid; padding-left: 1ex"> <br>If you want few selected eigen solutions of sparse matrix,<br>you should use sparse eigen solver. Take a look at'<br>slepc (<a href="http://www.grycap.upv.es/slepc/">http://www.grycap.upv.es/slepc/</a>)<br>or use slepc interface with arpack. <br><br>Hong<br><br><br>On Mon, 14 Jan 2008, Yujie wrote:<br><br>> Thank you for your advice.<br>> I have used -ksp_compute_eigenvalues_explicitly to get the eigen values.<br>> However, it is very very<br>> slow because the dimension of the matrix is about ten thousand. <br>><br>> Yujie<br>><br>> On 1/14/08, Matthew Knepley <<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>> wrote:<br>>><br>>> You can use<br>>><br>>><br>>> <a href="http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeEigenvaluesExplicitly.html"> http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeEigenvaluesExplicitly.html</a><br>>><br>>> with and without a preconditioner. We have not coded the SVD<br>>> counterpart, but you can use <br>>><br>>><br>>> <a href="http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeExplicitOperator.html">http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeExplicitOperator.html </a><br>>><br>>> and then call the LAPACK yourself.<br>>><br>>> Matt<br>>><br>>> On Jan 13, 2008 11:23 PM, Yujie <<a href="mailto:recrusader@gmail.com">recrusader@gmail.com</a>> wrote: <br>>>> Hi, everyone<br>>>><br>>>> I want to select iterative methods by observing the singular values<br>>>> decompostion of the matrix. However, I don't know how to get all the<br> >>> singular values of the matrix in PETSc. I know the command<br>>>> "-ksp_monitor_singular_value" may get the max and min singular values at<br>>>> each iteration. How to get the singular values of the matrix I want to <br>>>> solve? In addition, when I use the preconditioned iterative method, how<br>>> to<br>>>> get the singular values of the preconditioned iterative operator?<br>>>><br>>>> thanks a lot. <br>>>><br>>>> Regards,<br>>>> Yujie<br>>>><br>>><br>>><br>>><br>>> --<br>>> What most experimenters take for granted before they begin their<br>>> experiments is infinitely more interesting than any results to which <br>>> their experiments lead.<br>>> -- Norbert Wiener<br>>><br>>><br>><br><br></blockquote></div><br></blockquote></div><br></div></body></html>