[petsc-users] non-convergence for SNES ex5 and ex20
Jed Brown
jed at 59A2.org
Wed Jun 22 15:26:12 CDT 2011
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>
More information about the petsc-users
mailing list