<html><head><meta http-equiv="content-type" content="text/html; charset=us-ascii"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div><br></div> It would be useful to see the convergences inside the linear solve so perhaps start with <div><br></div><div>-ksp_monitor_true_residual </div><div><br></div><div>-fieldsplit_u_ksp_type richardson (this is to allow the monitor below to work)</div><div>-fieldsplit_u_ksp_max_its 1 </div><div>-fieldsplit_u_ksp_monitor</div><div><br></div><div>Perhaps others, Matt/Jed/Pierre/Stefano likely know better off the cuff than me.</div><div><br><div>We should have a convenience option like -pc_fieldsplit_schur_monitor similar to the -pc_fieldsplit_gkb_monitor</div><div><br></div><div><br></div><div><br><blockquote type="cite"><div>On Apr 13, 2023, at 4:33 PM, Alexander Lindsay <alexlindsay239@gmail.com> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr">Hi, I'm trying to solve steady Navier-Stokes for different Reynolds numbers. My options table<div><br></div><div>-dm_moose_fieldsplit_names u,p<br>-dm_moose_nfieldsplits 2<br>-fieldsplit_p_dm_moose_vars pressure<br>-fieldsplit_p_ksp_type preonly<br>-fieldsplit_p_pc_type jacobi<br>-fieldsplit_u_dm_moose_vars vel_x,vel_y<br>-fieldsplit_u_ksp_type preonly<br>-fieldsplit_u_pc_hypre_type boomeramg<br>-fieldsplit_u_pc_type hypre<br>-pc_fieldsplit_schur_fact_type full<br>-pc_fieldsplit_schur_precondition selfp<br>-pc_fieldsplit_type schur<br>-pc_type fieldsplit<br></div><div><br></div><div>works wonderfully for a low Reynolds number of 2.2. The solver performance crushes LU as I scale up the problem. However, not surprisingly this options table struggles when I bump the Reynolds number to 220. I've read that use of AIR (approximate ideal restriction) can improve performance for advection dominated problems. I've tried setting -pc_hypre_boomeramg_restriction_type 1 for a simple diffusion problem and the option works fine. However, when applying it to my field-split preconditioned Navier-Stokes system, I get immediate non-convergence:</div><div><br></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><div> 0 Nonlinear |R| = 1.033077e+03</div><div> 0 Linear |R| = 1.033077e+03</div><div> Linear solve did not converge due to DIVERGED_NANORINF iterations 0</div><div>Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0</div><div><br></div></blockquote>Does anyone have an idea as to why this might be happening? If not, I'd take a suggestion on where to set a breakpoint to start my own investigation. Alternatively, I welcome other preconditioning suggestions for an advection dominated problem.<div><br></div><div>Alex</div></div>
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