Did you use -ksp_converged_reason to determine why PETSc stopped iterating?
Matt On Wed, Dec 9, 2009 at 11:45 AM, Dominik Szczerba <dominik at itis.ethz.ch>wrote: > I am using > > -ksp_rtol 0 -ksp_atol 1e-6 (defaults for all the rest) > > and observe for most of the times convergence, as expected. > > Starting KSPSolve > 0 KSP Residual norm 6.315132950112e-04 > 1 KSP Residual norm 9.139539245601e-05 > 2 KSP Residual norm 1.869750068013e-05 > 3 KSP Residual norm 6.788145356909e-06 > 4 KSP Residual norm 1.729115712274e-06 > 5 KSP Residual norm 7.214445966641e-07 > solved in 2.328146e+00/4.144644e+00 s > solution converged in 5 iterations > ||Ax-b|| = 7.21445e-07 > > with ||...|| being residue computed on my own for a check. > > However, SOMETIMES, I do observe: > > Starting KSPSolve > 0 KSP Residual norm 1.228562818225e-02 > 1 KSP Residual norm 4.045833318123e-04 > 2 KSP Residual norm 6.589999324657e-05 > 3 KSP Residual norm 1.494849372638e-05 > 4 KSP Residual norm 4.311592172896e-06 > solved in 1.368086e+00/2.235830e+00 s > solution converged in 4 iterations > ||Ax-b|| = 4.31159e-06 > > which means that the iterations break sooner than they should. Again, this > is not often, but worries me why this should happen... Using or not > -ksp_converged_use_initial_residual_norm does not make any difference to > this behavior: the last output Residual norm is sometimes higher than the > requested atol. > > Any clarifications are highly appreciated. > > Dominik > -- 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20091209/d5272e27/attachment.htm>
