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https: //petsc. org/release/manualpages/KSP/KSPCR/ The preconditioner must be POSITIVE-DEFINITE and the operator POSITIVE-SEMIDEFINITE. KSPMINRES — PETSc 3. 21. 4 documentation petsc. org The operator and the preconditioner must be symmetric and
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caret-color: rgb(34, 40, 50); color: rgb(34, 40, 50); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; background-color: rgb(255, 255, 255);">The preconditioner must be POSITIVE-DEFINITE.</span></div><div><span style="font-size: 16px; caret-color: rgb(34, 40, 50); color: rgb(34, 40, 50); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; background-color: rgb(255, 255, 255);"><br></span></div><div><span style="font-size: 16px; caret-color: rgb(34, 40, 50); color: rgb(34, 40, 50); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; background-color: rgb(255, 255, 255);">Of course you can always use KSPGMRES or KSPBCGS</span></div><div><font color="#222832" face="-apple-system, BlinkMacSystemFont, Segoe UI, Helvetica Neue, Arial, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol"><span style="background-color: rgb(255, 255, 255);"><font size="3"><br id="lineBreakAtBeginningOfMessage"></font></span></font><div><br><blockquote type="cite"><div>On Aug 5, 2024, at 2:27 PM, Константин Мурусидзе <konstantin.murusidze@math.msu.ru> wrote:</div><br class="Apple-interchange-newline"><div>I know that matrix is symmetric, but it isn’t positive definite. Is it possible to solve such problem, maybe with another solver or preconditioner?<br><br>--<br>Отправлено из мобильной Яндекс Почты<br><br>05.08.2024, 18:51, "Barry Smith" <bsmith@petsc.dev>:<br><blockquote>PCFactorSetShiftType() only works for certain preconditioners, ILU. <div><br></div><div>If the matrix is not symmetric it also doesn't help.</div><div><br></div><div>Are you sure the matrix is symmetric positive definite?</div><div><br></div><div><br><div><blockquote><br><br></blockquote><div><blockquote><div>On Aug 5, 2024, at 4:43 AM, Константин Мурусидзе <<a href="mailto:konstantin.murusidze@math.msu.ru">konstantin.murusidze@math.msu.ru</a>> wrote:</div><br class="34bd394265c9c48ce7af3175baf9655dApple-interchange-newline"><div><div>After this procedure I saw "Linear solution did not converge due to DIVERGED_INDEFINITE_MAT". Then as shown on <a href="https://urldefense.us/v3/__https://petsc.org/main/manualpages/KSP/KSP_DIVERGED_INDEFINITE_PC/__;!!G_uCfscf7eWS!ZQFXJM_C7qCPyXSN6vUgcQaTYavgEpmvtDdWSpbY1dR7m_6DlTM1CF00dL26gVO4tjPEFFvV79SEmjS1OqyHDu0$">https://petsc.org/main/manualpages/KSP/KSP_DIVERGED_INDEFINITE_PC/</a> I wrote such line PetscCall(PCFactorSetShiftType(pc, MAT_SHIFT_POSITIVE_DEFINITE)); but nothing changed and I still have divergence</div><div><br></div><div><br></div><div>22.07.2024, 17:22, "Barry Smith" <<a href="mailto:bsmith@petsc.dev">bsmith@petsc.dev</a>>:</div><blockquote><div><br></div> Run with -ksp_monitor_true_residual -ksp_converged_reason -ksp_view to see why it is stopping at 38 iterations.<div><br></div><div> Barry</div><div><br id="cb7fb53d8024ab49fb3b5cd6352ceef1197d38eabd6a1f130a6b8653e70493blineBreakAtBeginningOfMessage"><div><br><blockquote><div>On Jul 22, 2024, at 7:37 AM, Константин Мурусидзе <<a href="mailto:konstantin.murusidze@math.msu.ru">konstantin.murusidze@math.msu.ru</a>> wrote:</div><br class="ac421fd3c4a8b6b63a73dee5a39abd5034bd394265c9c48ce7af3175baf9655dApple-interchange-newline"><div><div id="32a490392017c3f1a52f2e9921263c8a8853c347f276207aa3e14a8120b15c37pfptBannerrgpugnr" dir="ltr" style="background-color:rgb( 208 , 216 , 220 ) !important;border-radius:4px !important;border-top-color:rgb( 144 , 164 , 174 ) !important;border-top-style:solid !important;border-top-width:4px !important;display:block !important;font-family:'revert' !important;margin-bottom:16px !important;margin-left:0px !important;margin-right:0px !important;margin-top:16px !important;min-width:200px !important;padding-bottom:8px !important;padding-left:16px !important;padding-right:16px !important;padding-top:8px !important;text-align:left !important"><div id="32a490392017c3f1a52f2e9921263c8a8853c347f276207aa3e14a8120b15c37pfptBannerrgpugnr" style="display:block !important;float:left !important;font-family:'unset' !important;margin-bottom:1px !important;margin-left:0px !important;margin-right:0px !important;margin-top:0px !important;max-width:600px !important"><div id="32a490392017c3f1a52f2e9921263c8a8853c347f276207aa3e14a8120b15c37pfptBannerrgpugnr" style="background-color:rgb( 208 , 216 , 220 ) !important;display:block !important;font-family:'arial' , sans-serif !important;font-size:14px !important;font-weight:bold !important;line-height:18px !important;visibility:visible !important">This Message Is From an External Sender</div><div id="32a490392017c3f1a52f2e9921263c8a8853c347f276207aa3e14a8120b15c37pfptBannerrgpugnr" style="background-color:rgb( 208 , 216 , 220 ) !important;display:block !important;font-family:'arial' , sans-serif !important;font-size:12px !important;line-height:18px !important;margin-top:2px !important;visibility:visible !important">This message came from outside your organization.</div></div><div style="clear:both !important;display:block !important;font-size:0.01px !important;height:0px;line-height:0 !important;visibility:hidden !important"></div></div><div style="font-family:'helvetica';font-size:18px;font-style:normal;font-weight:400;text-align:start;text-decoration:none;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div>Good afternoon. I am a student at the Faculty of Mathematics and for my course work I need to solve SLAE with a relative accuracy of 1e-8 or more. To do this, I created the function PetscCall(KSPSetTolerances(ksp, 1.e-8, PETSC_DEFAULT, PETSC_DEFAULT, 100000));. But in the end, only 38 iterations were made and the relative norm ||Ax-b||/||b|| it turns out 4.54011. If you reply to my email, I can give you more information about the solver settings.</div></div></div></blockquote></div><br></div></blockquote></div></blockquote></div><br></div></div></blockquote></div></blockquote></div><br></div></body></html>