I wasn't expecting this. Try -pc_mg_type full -ksp_type richardson -mg_levels_pc_type bjacobi -mg_levels_ksp_type gmres -mg_levels_ksp_max_it 3 -mg_coarse_pc_factor_mat_solver_package superlu_dist -mg_coarse_pc_type lu -pc_mg_galerkin -pc_mg_levels 5 -pc_type mg -log_summary -pc_mg_log -ksp_monitor_true_residual -options_left -ksp_view -ksp_max_it 30
On Sep 30, 2013, at 8:00 PM, Michele Rosso <[email protected]> wrote: > Barry, > > sorry again for the very late answer. I tried all the variations you > proposed: all of them converge very slow , except the last one (CG instead of > fgmres) diverges. > I attached the diagnostics for the two options that convergence: each of the > attached files starts with a list of the options I used for the run. > As you pointed out earlier, the residual I used to require was too small, > therefore I increased atol to e-9. > After some tests, I noticed that any further increase of the absolute > tolerance changes significantly the solution. > What would you suggest to try next? > Thank you very much, > > Michele > > > > > > > On 09/24/2013 05:08 PM, Barry Smith wrote: >> Thanks. The balance of work on the different levels and across processes >> looks ok. So it is is a matter of improving the convergence rate. >> >> The initial residual norm is very small. Are you sure you need to decrease >> it to 10^-12 ???? >> >> Start with a really robust multigrid smoother use >> >> -pc_mg_type full -ksp_type fgmres -mg_levels_pc_type bjacobi >> -mg_levels_ksp_type gmres -mg_levels_ksp_max_it 3 PLUS >> -mg_coarse_pc_factor_mat_solver_package superlu_dist >> -mg_coarse_pc_type lu -pc_mg_galerkin -pc_mg_levels 5 -pc_mg_log -pc_type mg >> >> run with the -log_summary and -pc_mg_log >> >> Now back off a little on the smoother and use -mg_levels_pc_type sor instead >> how does that change the convergence and time. >> >> Back off even more an replace the -ksp_type fgmres with -ksp_type cg and the >> -mg_levels_ksp_type gmres with -mg_levels_ksp_type richardson how does >> that change the convergence and the time? >> >> There are some additional variants we can try based on the results from >> above. >> >> Barry >> >> >> >> On Sep 24, 2013, at 4:29 PM, Michele Rosso <[email protected]> wrote: >> >>> Barry, >>> >>> I re-rerun the test case with the option -pc_mg_log as you suggested. >>> I attached the new output ("final_new.txt'). >>> Thanks for your help. >>> >>> Michele >>> >>> On 09/23/2013 09:35 AM, Barry Smith wrote: >>>> Run with the additional option -pc_mg_log and send us the log file. >>>> >>>> Barry >>>> >>>> Maybe we should make this the default somehow. >>>> >>>> >>>> On Sep 23, 2013, at 10:55 AM, Michele Rosso <[email protected]> wrote: >>>> >>>>> Hi, >>>>> >>>>> I am successfully using PETSc to solve a 3D Poisson's equation with CG + >>>>> MG . Such equation arises from a projection algorithm for a multiphase >>>>> incompressible flow simulation. >>>>> I set up the solver as I was suggested to do in a previous thread >>>>> (title: "GAMG speed") and run a test case (liquid droplet with surface >>>>> tension falling under the effect of gravity in a quiescent fluid). >>>>> The solution of the Poisson Equation via multigrid is correct but it >>>>> becomes progressively slower and slower as the simulation progresses (I >>>>> am performing successive solves) due to an increase in the number of >>>>> iterations. >>>>> Since the solution of the Poisson equation is mission-critical, I need to >>>>> speed it up as much as I can. >>>>> Could you please help me out with this? >>>>> >>>>> I run the test case with the following options: >>>>> >>>>> -pc_type mg -pc_mg_galerkin -pc_mg_levels 5 -mg_levels_ksp_type >>>>> richardson -mg_levels_ksp_max_it 1 >>>>> -mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package >>>>> superlu_dist >>>>> -log_summary -ksp_view -ksp_monitor_true_residual -options_left >>>>> >>>>> Please find the diagnostic for the final solve in the attached file >>>>> "final.txt'. >>>>> Thank you, >>>>> >>>>> Michele >>>>> <final.txt> >>> <final_new.txt> >> > > <final1.txt><final2.txt>
