<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Do you want to refine the geometry or are you fine with the current one?<div>What kind of hardware are you planning on using (GPU, single-node…)?</div><div>Do you have a configuration for which LSC fails or does not give you good-enough performance?</div><div><br></div><div>Thanks,</div><div>Pierre</div><div><div><br><blockquote type="cite"><div>On 9 May 2025, at 9:08 PM, Mark Adams <mfadams@lbl.gov> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr">Hi Hardik,<div><br></div><div>The domain shape is not critical but the element shapes are. Your 100:1 domain aspect ratio is bad if you have N^3 mesh and thus element aspect ratios of 100:1. </div><div>If that is the case then you probably want to look at semi-coarsening multigrid.</div><div><br></div><div>Mark</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, May 9, 2025 at 9:55 AM Hardik Kothari <<a href="mailto:hardik.kothari@corintis.com">hardik.kothari@corintis.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div>Dear PETSc team,
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<div>We are solving the Stokes equations using PETSc (via Firedrake) on a highly anisotropic 3D domain (L_x=1, L_y=0.01, L_z=0.1).</div>
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<div>In this setup, standard Schur complement preconditioners using a mass inverse for pressure struggle to converge. We could solve the problem with the LSC preconditioner (solver parameters are shown in the script). </div>
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<div>We have the following questions:</div>
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<li>Why standard preconditioners struggle in such domains? </li><li>Why is the preconditioned residual norm for the Schur complement system much higher than the true residual norm?</li><li>Would you recommend alternative or more robust preconditioners for such geometries? </li></ul>
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<div>Thank you for your help. </div>
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<div>Best regards, </div>
<div>Hardik</div>
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