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Hello,
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<div class="">A00 comes from shell structures and discretized by FEM.</div>
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<div class="">Thanks,</div>
<div class="">Xiaofeng<br class="">
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<div class="">On Sep 27, 2022, at 17:48, Mark Adams <<a href="mailto:mfadams@lbl.gov" class="">mfadams@lbl.gov</a>> wrote:</div>
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<div dir="ltr" class="">what equations and discetizations are in A00?</div>
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<div dir="ltr" class="gmail_attr">On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何 <<a href="mailto:tlanyan@hotmail.com" class="">tlanyan@hotmail.com</a>> wrote:<br class="">
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<div style="overflow-wrap: break-word;" class="">Hi Barry,
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<div class="">A00 is formed from elliptic operator. </div>
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<div class="">I tried GAMG with A00, but it was extremely slow to solve the system with field-split preconditioner(I’m not sure I did it with the right way).</div>
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<div class="">Thanks,</div>
<div class="">Xiaofeng</div>
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<div class="">On Sep 26, 2022, at 23:11, Barry Smith <<a href="mailto:bsmith@petsc.dev" target="_blank" class="">bsmith@petsc.dev</a>> wrote:</div>
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<div class=""> What is your A00 operator? ILU is almost never a good choice for large scale problems. If it is an elliptic operator that using a PC of gamg may work well for the A00 preconditioner instead of ILU.</div>
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<div class=""> Barry</div>
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<div class=""> For moderate size problems you can use a PC type LU for AOO to help you understand the best preconditioner to use for the A11 (the Schur complement block), once you have a good preconditioner for the A11 block you would then go back and determine
a good preconditioner for the A00 block.<br class="">
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<div class="">On Sep 26, 2022, at 10:08 AM, 晓峰 何 <<a href="mailto:tlanyan@hotmail.com" target="_blank" class="">tlanyan@hotmail.com</a>> wrote:</div>
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<div style="overflow-wrap: break-word;" class="">Hello Jed,
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<div class="">The saddle point is due to Lagrange multipliers, thus the size of A11 is much smaller than A00.</div>
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<div class="">Best Regards,</div>
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<div class="">Xiaofeng</div>
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<div class="">On Sep 26, 2022, at 21:03, Jed Brown <<a href="mailto:jed@jedbrown.org" target="_blank" class="">jed@jedbrown.org</a>> wrote:</div>
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<div class=""><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;display:inline" class="">Lagrange
multipliers</span></div>
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