On Tue, May 3, 2011 at 15:50, <domenico.borzacchiello at univ-st-etienne.fr>wrote:
> Hi, > I'm solving Stokes equations with Pc FieldSplit and Schur Complement > Preconditioning. If I use a direct solver for the block A(0,0) and no > preconditioning for the Schur Complement (just fgmres), the outer solver > converges in typically 1-2 iterations and the inner solver for Schur > Complement in 10-15 iterations depending on the problem size. If I try to > precondition the Schur Complement with PCLSC (dev version) with direct > solution for the product A(2,1)*A(1,2) the Schur Complement solver takes > 350+ iterations to converge. What could be the cause of this behavior? > I've used LSC before (not in PETSC however) for transient Navier-Stokes > and it used to work fine. > > I suspect it is because you need -ksp_diagonal_scale. In petsc-dev, look at src/ksp/ksp/examples/tests/makefile, targets runex11 and runex11_2, for working configurations for a hard Stokes problem in geodynamics. LSC is normally described with the scaling "built in". Perhaps we should identify the fieldsplit/lsc combination and choose scaling automatically since it's usually necessary. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20110503/ce9df01b/attachment.html>
