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<p class="MsoNormal">Quite different:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">2-NORM(residualVec): 9802864883082.29<o:p></o:p></p>
<p class="MsoNormal">2-NORM(ksp): 6.802405785457120E-015<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Perhaps I’m doing something else wrong?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> Barry Smith <bsmith@petsc.dev> <br>
<b>Sent:</b> Monday, December 6, 2021 11:58 AM<br>
<b>To:</b> Fischer, Greg A. <fischega@westinghouse.com><br>
<b>Cc:</b> petsc-users@mcs.anl.gov<br>
<b>Subject:</b> Re: [petsc-users] KSPBuildResidual and KSPType compatibility<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:red">[External Email]</span> <o:p></o:p></p>
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<p class="MsoNormal"> This algorithm computes the residual norms indirectly (this is part of the "trick" of the algorithm to reduce the number of global reductions needed), thus they may not match the actual residual norm computed by || b - A x ||. How different
are your values? <o:p></o:p></p>
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<p class="MsoNormal"> Barry<o:p></o:p></p>
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<p class="MsoNormal">On Dec 6, 2021, at 11:19 AM, Fischer, Greg A. via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hello petsc-users,<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">I would like to check convergence against the infinity norm, so I defined my own convergence test routine with KSPSetConvergenceTest. (I understand that it may be computationally expensive.)<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">I would like to do this with the “ibcgs” method. When I use KSPBuildResidual and calculate the NORM_2 against the output vector, I get a value that differs from the 2-norm that gets passed into the convergence test function. However, when
I switch to the “gcr” method, the value I calculate matches the function input value.<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">Is the KSPBuildResidual function only compatible with a subset of the KSPType methods? If I want to evaluate convergence against the infinity norm, do I need to set KSPSetInitialGuessNonzero and continually re-start the solver with a lower
tolerance values until I get a satisfactory value of the infinity norm?<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Greg<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:gray"><br>
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