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Hello PETSc Community,</div>
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I am trying to understand the scaling behaviour of AMG methods in PETSc (Hypre for now) and how many DOFs/Rank are needed for a performant AMG solve.</div>
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I’m currently conducting weak scaling tests using <code>src/snes/tutorials/ex12.c</code> in 3D, applying Dirichlet BCs with FEM at P=1. The tests keep DOFs per processor constant while increasing the mesh size and processor count, specifically:</div>
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<b>20000 and 80000 DOF/RANK</b> configurations.</li><li style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Running SNES twice, using GMRES with a tolerance of 1e-5 and preconditioning with Hypre-BoomerAMG.</li></ul>
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Unfortunately, parallel efficiency degrades noticeably with increased processor counts. Are there any insights or rules of thumb for using AMG more effectively? I have been looking at this issue for a while now and would love to engage in a further discussion.
Please find below the weak scaling results and the options I use to run the tests.</div>
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<img id="image_0" width="651" height="334" size="119488" contenttype="image/png" style="width: 651px; height: 334px;" data-outlook-trace="F:1|T:1" src="cid:b3265a6e-baed-4fc1-a58d-0eebbb7de5a4"></div>
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<b>#Run type</b></div>
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-run_type full</div>
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-petscpartitioner_type simple</div>
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<b>#Mesh settings</b></div>
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-dm_plex_dim 3</div>
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-dm_plex_simplex 1</div>
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-dm_refine 5 #Varied this</div>
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-dm_plex_box_faces 6,6,6</div>
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<b>#BCs and FEM space</b></div>
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-bc_type dirichlet</div>
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-petscspace_degree 1</div>
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<b>#Solver settings</b></div>
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-snes_max_it 2</div>
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-ksp_type gmres</div>
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-ksp_rtol 1.0e-5</div>
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#Same settings as what we use for LOR</div>
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-pc_type hypre</div>
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-pc_hypre_type boomeramg</div>
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-pc_hypre_boomeramg_coarsen_type hmis</div>
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-pc_hypre_boomeramg_relax_type_all symmetric-sor/jacobi</div>
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-pc_hypre_boomeramg_strong_threshold 0.7</div>
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-pc_hypre_boomeramg_interp_type ext+i</div>
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-pc_hypre_boomeramg_P_max 2</div>
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-pc_hypre_boomeramg_truncfactor 0.3</div>
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Best,</div>
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Parv</div>
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