I use: run: -@${MPIEXEC} -n 1 ./ex56 -ne 49 -pc_gamg_verbose -alpha 1.e-3 -ksp_monitor -ksp_type cg -pc_gamg_type sa -ksp_rtol 1.e-10
plus -mg_levels_ksp_max_it to adjust smoothing. src/ksp/ksp/examples/tutorials has ex54 ex55 and ex56 that do a 2D scalar Lapacian, 2D elasticity and 3D elasticity respectively. -ne is the number of elements on a side so for the 2D problems '-ne 100' is decent and for 3D '-ne 49' is pretty big unless you are running in parallel. I've just started using -ksp_rtol 1.e-10 and retested all of these test and am seeing a very slight improvement going from 1 to 4. I would expect to see a significant drop, say 25%, in the number of iterations going from 1 to 2. The < 5% that I am seeing seems too low but I'm not 100% sure -- maybe there is nothing wrong ... Mark On Dec 26, 2011, at 10:41 AM, Jed Brown wrote: > On Mon, Dec 26, 2011 at 00:07, Mark F. Adams <mark.adams at columbia.edu> > wrote: >> Can you show me an example? I have certainly seen it make a different for >> other problems. > > OK, well we need to think about this then. Maybe we can take a look at it at > Brown in January. There must be some bad interaction in the way that I'm > using it. The code is around 662 in gamg.c. > > Can you tell me how to run an example that shows this behavior? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20111226/5e6ac292/attachment.html>