<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Barry, <div class=""><br class=""></div><div class=""> Here are some quick numbers with the following options on 4 CPUs and 543,606 dofs: </div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-stretch: normal; font-size: 10px; line-height: normal; font-family: Monaco; color: rgb(242, 242, 242); background-color: rgba(0, 0, 0, 0.85098);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">-mg_levels_ksp_max_it 4 -pc_gamg_square_graph 1 -pc_gamg_threshold 0.</span></div></div><div class=""><br class=""></div><div class=""> #levels | #KSP Iters</div><div class="">———————————</div><div class=""> 2 | 18</div><div class=""> 3 | 18</div><div class=""><div class=""> 4 | 40</div><div class=""><div class=""> 5 | 59</div></div><div class=""><br class=""></div><div>-Manav</div><div><br class=""></div><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 29, 2018, at 2:06 PM, Smith, Barry F. <<a href="mailto:bsmith@mcs.anl.gov" class="">bsmith@mcs.anl.gov</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class=""> Exactly how much does it increase with number of levels? Send a chart number of levels and number of iterations. With say -mg_levels_ksp_maxit 4<br class=""><br class=""> Thanks<br class=""><br class=""> Barry<br class=""><br class=""><br class=""><br class=""><br class=""><blockquote type="cite" class="">On Oct 29, 2018, at 12:59 PM, Manav Bhatia <<a href="mailto:bhatiamanav@gmail.com" class="">bhatiamanav@gmail.com</a>> wrote:<br class=""><br class="">Thanks for the clarification. <br class=""><br class="">I also observed that the number of KSP iterations increases with an increase in the levels of AMG. Is this true, in general, for all/most applications? <br class=""><br class="">-Manav<br class=""><br class=""><blockquote type="cite" class="">On Oct 29, 2018, at 12:53 PM, Jed Brown <<a href="mailto:jed@jedbrown.org" class="">jed@jedbrown.org</a>> wrote:<br class=""><br class="">Manav Bhatia <<a href="mailto:bhatiamanav@gmail.com" class="">bhatiamanav@gmail.com</a>> writes:<br class=""><br class=""><blockquote type="cite" class="">Thanks, Jed. <br class=""><br class="">The description says: “ Square the graph, ie. compute A'*A before aggregating it"<br class=""><br class="">What is A here? <br class=""></blockquote><br class="">The original matrix, or its "graph" (your 6x6 blocks condensed to scalars).<br class=""><br class=""><blockquote type="cite" class="">What is the impact of setting this to 0, which led to a very significant increase in the CPU time in my case? <br class=""></blockquote><br class="">The aggregates are formed on the connectivity of your original matrix,<br class="">so root nodes are aggregated only with their first neighbors, resulting<br class="">in slower coarsening.<br class=""></blockquote><br class=""></blockquote><br class=""></div></div></blockquote></div><br class=""></div></body></html>