On Wed, Jun 22, 2011 at 17:32, Qian Zhu <qzhu at mcs.anl.gov> wrote: > Thanks for the reply, Jed. I worked on ex27 so I know setting certain > values for the input parameters can make the case converge/non-converge...I > am just wondering whether this is also true with ex5 and ex20 (We picked > them for other interesting characteristics).
Well, ex5 is a really simple problem which converges pretty easily when lambda < 6.81 (the bifurcation point). I don't know how hard ex20 is, but you could certainly increase the power beta. What characteristics are you looking for? Asking for a solver that doesn't converge just seems like an odd request considering that we spend lots of time figuring out how to make them converge robustly. > Which examples are solving the Stokers problem? src/ksp/ksp/examples/tutorials/ex43.c This will happily not converge: $ ./ex43 -mx 40 -my 40 -c_str 2 -sinker_eta0 1e-8 -sinker_eta1 1 -stokes_ksp_monitor_true_residual -stokes_ksp_type fgmres Run this to see some configurations that do work: $ make -n runex43 runex43_2 The discretization above is not particularly robust, but is relatively easy to solve. This one is harder [1] src/ksp/ksp/examples/tests/ex11.c This will pretend to converge, but the true residuals are nonsense. ./ex11 -f $DATAFILESPATH/matrices/underworld32.gz -fc_ksp_monitor_true_residual If you add -fc_ksp_type fgmres to the above, it will stop pretending (and just not converge). To see some solver configurations that work, use $ make -n runex11 runex11_2 [1] Follow the directions here to get the test matrix: http://www.mcs.anl.gov/petsc/petsc-2/documentation/faq.html#datafiles -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110622/fd17f1c7/attachment.htm>
