Hi, Matt, Thanks for the help. I got it. Have a nice day Best wishes Zhengyong
On Tue, Apr 3, 2012 at 11:44 PM, Matthew Knepley <knepley at gmail.com> wrote: > On Tue, Apr 3, 2012 at 4:40 PM, RenZhengYong <renzhengyong at gmail.com>wrote: > >> Hi, Jed, >> Thanks for your quick reply and have a nice day. >> >> My problem is to solve a hybrid FEM-BEM problem, so one sub-matrix from >> BEM is fully dense and one from BEM-FEM is partially dense. I managed to >> used a multi-level fast multpole method to compute the product of my entire >> system matrix with a given vector. And I can find a quite good problem >> dependent approximation B to my system matrix *A*. >> >> My next purpose to speed up the convergence rate of GMRES using this >> operator *B*. In my code, the expensive of storage of the far field >> interaction from BEM part is avoided. And I can explicitly form the sparse >> matrix *B*. So, could I ask you: >> how to give the sparse matrix *B* to petsc?. Because *B* is sparse, I >> prefer to fully LU decomposition to solve the preconditioned problem *B*z=c. >> >> > > Give B as the preconditioner matrix, > > KSPSetOperators(ksp, A, B, ...) > > Matt > > >> Best wishes >> Zhengyong >> >> On Tue, Apr 3, 2012 at 11:28 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote: >> >>> On Tue, Apr 3, 2012 at 14:25, RenZhengYong <renzhengyong at gmail.com>wrote: >>> >>>> I have a question to ask for your suggestions which is to solve Ax=b >>>> using GMRES, >>>> here A is partially dense. Using petsc, I successfully used the >>>> matrix-free approach to solve >>>> it so that the expensive storage of A is avoided. My question is could >>>> I offer an matrix B >>>> (which is sparse matrix and good approximation to A) so that the >>>> convergence rate of >>>> GMRES can be speed up. >>>> >>> >>> Certainly, but the challenge is to find this other operator. You could >>> try sparse approximate methods to approximate either the operator or its >>> inverse. Other approaches would typically involve further knowledge of your >>> problem. >>> >> >> >> >> -- >> Zhengyong Ren >> AUG Group, Institute of Geophysics >> Department of Geosciences, ETH Zurich >> NO H 47 Sonneggstrasse 5 >> CH-8092, Z?rich, Switzerland >> Tel: +41 44 633 37561 >> e-mail: zhengyong.ren at aug.ig.erdw.ethz.ch >> Gmail: renzhengyong at gmail.com >> > > > > -- > 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 > -- Zhengyong Ren AUG Group, Institute of Geophysics Department of Geosciences, ETH Zurich NO H 47 Sonneggstrasse 5 CH-8092, Z?rich, Switzerland Tel: +41 44 633 37561 e-mail: zhengyong.ren at aug.ig.erdw.ethz.ch Gmail: renzhengyong at gmail.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120403/3c60b66b/attachment.htm>
