Hi, Thanks for your assistance.
Switching to BiCGStab (-ksp_type bcgs) doesn't improve convergence and shows the same symptoms (residual with frequent oscillations). Using fieldsplit as Jens suggests doesn't help either; residual doesn't go below 1e-3 even after 1000 iterations. Using GMRES makes the oscillations disappear, but the residual doesn't converge either. Cheers, Dana On Sat, Feb 1, 2014 at 4:28 PM, David Knezevic <[email protected]>wrote: > Thanks Jens, we'll try this next week. > > > > On 02/01/2014 04:06 AM, Jens Lohne Eftang wrote: > > Hi, > > > > I used these arguments for 3D elasticity and they seemed to work well > > also in combination with DirichletBoundary (why does that break > symmetry?) > > > > -ksp_type cg > > -pc_type fieldsplit > > -pc_fieldsplit_block_size 3 > > -fieldsplit_pc_type hypre > > -fieldsplit_pc_hypre_type boomeramg > > -fieldsplit_pc_hypre_boomeramg_strong_threshold 0.7 > > -pc_fieldsplit_0 0,1,2 > > -ksp_atol 1e-11 > > -ksp_rtol 1e-11 > > -pc_fieldsplit_type symmetric_multiplicative > > > > It is key to use the fieldsplit preconditioner in order to be able to > > exploit smoothness within each field component. If it's 2D elasticity I > > believe you'd have to modify to -pc_fieldsplit_block_size 2 and > > -pc_fieldsplit_0 0,1. > > > > I was able to solve a problem with tens of millions dofs in 90 CG > > iterations using these parameters. > > > > Best, > > Jens > > > > On 01/31/2014 11:11 PM, David Knezevic wrote: > >> On 01/31/2014 12:36 PM, John Peterson wrote: > >>>> Hello, > >>>> > >>>> I'm trying to solve a linear elasticity problem based on a > tetraheadral > >>>> mesh with over a million degrees of freedom. > >>>> > >>>> I've been using the LU solver in MUMPS but I'm now forced to switch > to an > >>>> iterative solver because of the memory requirements of that solver. > >>>> > >>>> CG and BoomerAMG in hypre seem to be a good combination, but I've not > been > >>>> able to achieve convergence. The residual never goes below 1 even > after > >>>> several thousand iterations and shows high oscillations. > >>>> > >>>> The parameters I'm using are > >>>> -ksp_type cg > >>>> -ksp_monitor > >>>> -ksp_converged_reason > >>>> -pc_type hypre > >>>> -pc_hypre_type boomeramg > >>>> -pc_hypre_boomeramg_strong_threshold 0.7 > >>>> -log_summary > >>>> > >>> First thing I would think of is that the problem isn't actually > symmetric > >>> even though logically it should be? > >>> > >>> Does it work any better with -ksp_type bcgs? > >>> > >>> > >>> > >>>> -eps_monitor > >>>> -st_type sinvert > >>>> > >>> Is this an eigenvalue problem too? > >> Dana is working with me on this. It's not an eigenproblem, so > >> "-eps_monitor -st_type sinvert" isn't meant to be there (but it those > >> options would've just been ignored I believe). > >> > >> Regarding symmetry: That's a good thought. The PDE is linear elasticity, > >> hence it's symmetric. But we enforce boundary conditions using > >> DirchletBoundary, so that'll ruin symmetry on the Dirichlet rows/cols. > >> Not sure if that's the problem here or not, but Dana will try "-ksp_type > >> bcgs" to see if that helps convergence. > >> > >> Thanks, > >> David > >> > >> > >> > >> > >> > ------------------------------------------------------------------------------ > >> WatchGuard Dimension instantly turns raw network data into actionable > >> security intelligence. It gives you real-time visual feedback on key > >> security issues and trends. 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