On 09/13/2012 07:22 PM, Jed Brown wrote: > On Thu, Sep 13, 2012 at 4:16 PM, David Knezevic > <[email protected] <mailto:[email protected]>> wrote: > > > Calling > > ./systems_of_equations_ex6-opt -ksp_type cg > > runs fast, but gives the wrong answer > > > > > > That's alarming... > > > > Is ICC the default preconditioner with CG? If not, give that a try > > (maybe with -pc_factor_levels 4 or something) > > > ahh, "-pc_type icc" did the trick, thanks! I'll add that to the > Makefile. > > > Use -ksp_monitor_true_residual. If ILU does something meaningfully > different from ICC, the system is almost certainly nonsymmetric. Check > boundary conditions. > > But for elasticity, it's well worth getting algebraic multigrid > working. Hypre does classical AMG which isn't much good for systems. > Use petsc-3.3 or later and call MatSetNearNullSpace() to provide the > rigid body modes, then use either -pc_type gamg or -pc_type ml. Either > should do fine (and can usually be tuned to do about the same > algorithm, but have different defaults). If you use a nodal basis, you > can stuff the nodal coordinates in a vector with suitable block size > and call MatNullSpaceCreateRigidBody().
OK, thanks, I'll look into this. David ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://ad.doubleclick.net/clk;258768047;13503038;j? http://info.appdynamics.com/FreeJavaPerformanceDownload.html _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
