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<div class="moz-cite-prefix">Dear Matt,</div>
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<div class="moz-cite-prefix">thanks for the fast response. That makes perfect sense to me.
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<div class="moz-cite-prefix">Best regards</div>
<div class="moz-cite-prefix">Elias<br>
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<div class="moz-cite-prefix">Am 06.07.22 um 14:35 schrieb Matthew Knepley:<br>
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<div dir="ltr">On Wed, Jul 6, 2022 at 7:46 AM Karabelas, Elias (<a href="mailto:elias.karabelas@uni-graz.at" moz-do-not-send="true">elias.karabelas@uni-graz.at</a>) <<a href="mailto:elias.karabelas@uni-graz.at" moz-do-not-send="true">elias.karabelas@uni-graz.at</a>>
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<p><font size="4"><font face="monospace">Dear all,</font></font></p>
<p><font size="4"><font face="monospace">I don't know if this is a bug, but I observed that when using GMRES with AGG-PCGAMG as preconditioner Dirichlet boundary conditions don't seem to be exactly fulfilled.</font></font></p>
<p><font size="4"><font face="monospace">My Matrix has zero rows and cols with 1 on the diagonal where I have dirichlet-bcs in my FE-mesh and I would expect that the eqs in this rows can be exactly fulfilled (as u_i = g_i) there.</font></font></p>
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<div>I would not expect aggregation to be exact here, but only within the iteration tolerance. If instead you eliminate those variables, you can maintain algebraic exactness.</div>
<div>This is what we do in examples, like SNES ex56.</div>
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<div> Thanks,</div>
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<div> Matt</div>
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<p><font size="4"><font face="monospace">However, when I solve A*x = b with the above solver I only get u_i = g_i + error in that part of the vector. Switching from pc_gamg_type agg to pc_gamg_type classical cures this problem, but the classical is not advertised
in the user manual.</font></font></p>
<p>These are the options I'm currently using:</p>
<p>-ksp_type gmres<br>
-ksp_pc_side right<br>
-pc_type gamg<br>
-pc_gamg_type agg [or classical]<br>
-pc_gamg_sym_graph 1<br>
-pc_gamg_square_graph 1<br>
-pc_gamg_agg_nsmooths 1<br>
-pc_gamg_threshold 0.01<br>
-pc_mg_cycles v<br>
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<p>Iteration counts are basically the same.</p>
<p>Best regards</p>
<p>Elias<br>
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<pre cols="72">--
Dr. Elias Karabelas
Research Associate
University of Graz
Institute of Mathematics and Scientific Computing
Heinrichstraße 36
A-8010 Graz
Austria
Phone: +43 316 380 8546
Email: <a href="mailto:elias.karabelas@uni-graz.at" target="_blank" moz-do-not-send="true">elias.karabelas@uni-graz.at</a>
Web: <a href="https://ccl.medunigraz.at/" target="_blank" moz-do-not-send="true">https://ccl.medunigraz.at/</a></pre>
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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>
-- Norbert Wiener</div>
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<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" moz-do-not-send="true">https://www.cse.buffalo.edu/~knepley/</a><br>
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<pre class="moz-signature" cols="72">--
Dr. Elias Karabelas
Research Associate
University of Graz
Institute of Mathematics and Scientific Computing
Heinrichstraße 36
A-8010 Graz
Austria
Phone: +43 316 380 8546
Email: <a class="moz-txt-link-abbreviated" href="mailto:elias.karabelas@uni-graz.at">elias.karabelas@uni-graz.at</a>
Web: <a class="moz-txt-link-freetext" href="https://ccl.medunigraz.at/">https://ccl.medunigraz.at/</a></pre>
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