Dear petsc users, <br><br>I have a question to ask for your suggestions which is to solve Ax=b using GMRES, <br>here A is partially dense.  Using petsc, I successfully used the matrix-free approach to solve<br>it so that the expensive storage of A is avoided.  My question is could I offer an matrix B <br>
(which is sparse matrix and good approximation to A) so that the convergence rate of <br>GMRES can be speed up. <br><br>Best wishes<br>Zhengyong <br><br clear="all"><br>-- <br>Zhengyong Ren<br>AUG Group, Institute of Geophysics<br>
Department of Geosciences, ETH Zurich<br>NO H 47 Sonneggstrasse 5<br>CH-8092, Zürich, Switzerland<br>Tel: +41 44 633 37561<br>e-mail: <a href="mailto:zhengyong.ren@aug.ig.erdw.ethz.ch">zhengyong.ren@aug.ig.erdw.ethz.ch</a><br>
Gmail: <a href="mailto:renzhengyong@gmail.com">renzhengyong@gmail.com</a><br>