On Dec 21, 2011, at 9:01 PM, Mengda Wu wrote: > Hi all, > > I am trying to solve an overdetermined system using Petsc. I am using > un-preconditioned LSQR but it seems that it converges slowly. I am woer > ndering what preconditioner may improve the convergence. Or > are there any other ksp I can use?
What are the typical sizes of the matrix? Note that when running with preconditioning you need to call KSPSetOperators(ksp,A,B,DIFFERENT_NONZERO_PATTERN) where B is A'*A which can be obtained with MatMatMultTranspose(). (in petsc-3.2). Then you can try -pc_type lu -pc_type ilu or any other preconditioner. Barry > > Thanks, > Mengda
