On Wed, Dec 9, 2009 at 12:49 PM, Dominik Szczerba <dominik at itis.ethz.ch>wrote:
> Excellent point. Where it broke the reason was: > > Starting KSPSolve > 0 KSP Residual norm 7.841852910113e-04 > 1 KSP Residual norm 8.927576540999e-05 > 2 KSP Residual norm 1.694401713084e-05 > 3 KSP Residual norm 5.069425875318e-06 > Linear solve converged due to CONVERGED_RTOL iterations 3 > > which I assume means that the norm became exactly 0 > I don't think so. It would have printed that for the residual. > HOWEVER: putting -ksp_rtol -1 still does not eliminate the problem. Any > further suggestions? > You -ksp_view to see the tolerances used. Matt > Dominik > > Matthew Knepley wrote: > >> 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<mailto: >> 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 >> > > -- 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/20091209/0b498838/attachment.htm>
