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<p>Dear Jose and Matt,<br>
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<p>I thank you very much for your super-fast answers. And I apologize for not having checked the list of changes.<br>
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<div style="margin:0px"><font size="3" face="Calibri,sans-serif">Best regards, </font>
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<div style="margin:0px"><font face="Calibri,sans-serif"><font size="3" style="">Nicolas<br>
<span style="font-size:11pt">--</span></font><br>
</font><font size="2" face="Arial,sans-serif" color="#ff8100"><span style="font-size:9pt"><b>Nicolas Tardieu</b></span></font><br>
<div style="margin:0px"><font size="2" face="Calibri,sans-serif"><span style="font-size:11pt"><font size="1" face="Arial,sans-serif" color="#ff8100"><span style="font-size:8pt"><b>Ingénieur Chercheur
</b></span></font><font size="1" face="Arial,sans-serif" color="#ff8100"><span style="font-size:8pt"><b><br>
Groupe Dynamique des Equipements - T6B</b></span></font></span></font></div>
<div style="margin:0px"><font size="2" face="Calibri,sans-serif"><span style="font-size:11pt"><font size="1" face="Arial,sans-serif" color="#0062e1"><span lang="en-US" style="font-size:8pt">EDF - R&D Dpt ERMES</span></font><font size="1" face="Helv,sans-serif" color="#0062e1"><span lang="en-US" style="font-size:2pt"><br>
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<div style="margin:0px"><font size="2" face="Calibri,sans-serif"><span style="font-size:11pt"><font size="1" face="Arial,sans-serif" color="#0062e1"><span lang="en-US" style="font-size:8pt"><b>nicolas.tardieu@edf.fr</b></span></font></span></font></div>
<div dir="ltr" style="margin:0px"><font size="2" face="Calibri,sans-serif"><span style="font-size:11pt"><font size="1" face="Arial,sans-serif" color="#0062e1"><span lang="en-US" style="font-size:8pt">Tél. : 01 78 19 37 49<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>De :</b> knepley@gmail.com <knepley@gmail.com><br>
<b>Envoyé :</b> mardi 28 septembre 2021 14:54<br>
<b>À :</b> TARDIEU Nicolas<br>
<b>Cc :</b> petsc-users@mcs.anl.gov<br>
<b>Objet :</b> Re: [petsc-users] GMRES Breakdown</font>
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<div dir="ltr">On Tue, Sep 28, 2021 at 8:39 AM TARDIEU Nicolas via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<br>
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<div>Dear PETSc Team,<br>
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<div>We, code_aster's development team, are using PETSc in our application for years now, mainly for the KSP et PC features. We run tests cases every week without problems.<br>
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After upgrading from PETSc 3.12.3 to <span style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; background-color:rgb(255,255,255)">3.15.3, a test case using GMRES failed with KSP_DIVERGED_BREAKDOWN. By rolling back to 3.12.3, we have checked
that the upgrade is the origin of the failure.</span>
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<div>We know this can occur with GMRES but it is the first time we are facing this situation. <br>
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<p>Is it a bug ? If yes, how can we help to fix it ? If no, what can we do ? Could the flexible version of GMRES be an alternative ?</p>
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<div>This is not a bug, but we did change the operation. We now check whether there is a significant residual spike after a restart. We</div>
<div>want to let the user know that this likely means that the solver is inappropriate for the problem. As Jose notes, you can turn off this</div>
<div>behavior.</div>
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<div> Thanks,</div>
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<div> Matt</div>
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<div style="margin:0px"><font size="3" face="Calibri,sans-serif">Best regards, </font>
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<div style="margin:0px"><font face="Calibri,sans-serif"><font size="3">Nicolas<br>
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</font><font size="2" face="Arial,sans-serif" color="#ff8100"><span style="font-size:9pt"><b>Nicolas Tardieu</b></span></font><br>
<div style="margin:0px"><font size="2" face="Calibri,sans-serif"><span style="font-size:11pt"><font size="1" face="Arial,sans-serif" color="#ff8100"><span style="font-size:8pt"><b>Ing, PhD</b></span></font></span></font></div>
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<div>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
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