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<div class="elementToProof"><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 16px; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">Sequential solver</span><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"> superlu
ILU supports </span><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">drop tolerance.
For example, petsc/src/ksp/ksp/tutorials/ex2.c:</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">./ex2
-pc_type ilu -pc_factor_mat_solver_type superlu -help |grep superlu</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">...</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">-mat_superlu_ilu_droptol:
<now 0.0001 : formerly 0.0001>: ILU_DropTol (None)</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"><br>
</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">i.e.,
you can run it as</span></div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">$
./ex2 -pc_type ilu -pc_factor_mat_solver_type superlu -mat_superlu_ilu_droptol 0.0001 -ksp_monitor</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"> 0 KSP Residual norm 7.483267010387e+00</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"> 1 KSP Residual norm 5.109625265233e-05</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);">Norm of error 5.10959e-05 iterations 1</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"><br>
</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);">$ ./ex2 -pc_type ilu -pc_factor_mat_solver_type superlu -mat_superlu_ilu_droptol
0.001 -ksp_monitor</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"> 0 KSP Residual norm 7.473227154663e+00</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"> 1 KSP Residual norm 5.916533165499e-03</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36);"> 2 KSP Residual norm 1.638603182685e-06</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Norm of error 1.6387e-06
iterations 2</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"><br>
</span></div>
<div><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Hong</span></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> petsc-users <petsc-users-bounces@mcs.anl.gov> on behalf of Barry Smith <bsmith@petsc.dev><br>
<b>Sent:</b> Tuesday, February 27, 2024 11:27 AM<br>
<b>To:</b> Константин Мурусидзе <konstantin.murusidze@math.msu.ru><br>
<b>Cc:</b> petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov><br>
<b>Subject:</b> Re: [petsc-users] Problem of using PCFactorSetDropTolerance</font>
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We don't consider drop tolerance preconditioners as reliable or robust so I don't see anyone implementing it. On Feb 27, 2024, at 10: 11 AM, Константин Мурусидзе <konstantin. murusidze@ math. msu. ru> wrote: Thank you! Should we expect it
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We don't consider drop tolerance preconditioners as reliable or robust so I don't see anyone implementing it.
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<div>On Feb 27, 2024, at 10:11 AM, Константин Мурусидзе <konstantin.murusidze@math.msu.ru> wrote:</div>
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<div>Thank you! Should we expect it to appear in the near future?</div>
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<div>27.02.2024, 18:07, "Barry Smith" <bsmith@petsc.dev>:</div>
<blockquote>
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I'm sorry for the confusion. PETSc does not have a drop tolerance ILU so this function does nothing as you've noted.
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<div> Barry</div>
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<div>On Feb 27, 2024, at 7:27 AM, Константин Мурусидзе <<a href="mailto:konstantin.murusidze@math.msu.ru">konstantin.murusidze@math.msu.ru</a>> wrote:</div>
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Hello! I have such problem, while solving linear system and using PCFactorSetDropTolerance. As I understand this function could significantly reduce number of iterations of system of solution, but there is no iterations decreasing.<span style="background-color:transparent">I
had try a lot of options for this function, but there is no result</span>
<div>Could you suggest me if I have some mistake, while I setting up the preconditioner?</div>
<div> </div>
<div> PetscCall(KSPSetType(ksp, KSPCG));</div>
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<div>
<div> PetscCall(KSPSetInitialGuessNonzero(ksp,PETSC_TRUE));</div>
<div> PetscCall(KSPSetNormType(ksp, KSP_NORM_DEFAULT));</div>
<div> PetscCall(KSPCGSetType(ksp, KSP_CG_SYMMETRIC));</div>
</div>
<div> </div>
<div>
<div> PetscCall(KSPGetPC(ksp, &pc));</div>
<div> PetscCall(PCSetType(pc, PCILU));</div>
<div> PetscCall(PCFactorSetShiftType(pc, MAT_SHIFT_POSITIVE_DEFINITE));</div>
<div> </div>
<div> PetscCall(PCFactorSetLevels(pc, 2));</div>
<div> PetscCall(PCFactorSetReuseOrdering(pc,PETSC_TRUE));</div>
<div> PetscCall(PCFactorSetDropTolerance(pc, 1.e-5, 1.e-3, 10000));</div>
<div> PetscCall(PCFactorSetZeroPivot(pc, 1.e-3));</div>
<div> PetscCall(KSPSetTolerances(ksp, 1.e-8, 1.e-8, PETSC_DEFAULT, PETSC_DEFAULT));</div>
</div>
<div> </div>
<div>
<div> PetscCall(KSPSetFromOptions(ksp));</div>
</div>
<div> </div>
<div>
<div> PetscCall(KSPSolve(ksp, b, x));</div>
<div> PetscCall(KSPGetIterationNumber(ksp, &its));</div>
</div>
</div>
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