<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=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 6 Nov 2019, at 7:44 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><div dir="ltr" class="">On Wed, Nov 6, 2019 at 1:32 PM Pierre Jolivet via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov" class="">petsc-dev@mcs.anl.gov</a>> wrote:<br class=""></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><div class=""><blockquote type="cite" class=""><div class="">On 6 Nov 2019, at 7:30 PM, Fande Kong <<a href="mailto:fdkong.jd@gmail.com" target="_blank" class="">fdkong.jd@gmail.com</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class=""><div dir="ltr" class="">Even if both the linear operator and the preconditioner operator are symmetric, the preconditioned operator by RAS will NOT be symmetric so that CG is not applicable. <div class=""><br class=""></div><div class="">RAS keeps overlapping elements during restriction but discards them when doing interpolation, which leads to an unsymmetric preconditioned operator.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Of course.</div><div class="">What’s your point?</div></div></div></blockquote><div class=""><br class=""></div><div class="">I guess Fande's point is that we should consider switching to CG or MINRES, since we are being careful about the PC.</div></div></div></div></blockquote><div><br class=""></div><div>OK, that would make sense.</div><div>Still, it is known that in some cases, ASM will not converge when RAS will (OK, that’s only true with KSPRICHARDSON…), so I’m a little bit sceptical on the default switch to BASIC.</div><div><br class=""></div><div>Thanks,</div><div>Pierre</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><div class="gmail_quote"><div class=""> <span class="Apple-converted-space"> </span>Thanks,</div><div class=""><br class=""></div><div class=""> Matt</div><div class=""> </div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><div class=""><div class="">Thanks,</div><div class="">Pierre</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div dir="ltr" class=""><div class="">Fande,<br class=""><div class=""><br class=""></div><div class=""> </div></div></div></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Nov 6, 2019 at 11:13 AM Pierre Jolivet via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov" target="_blank" class="">petsc-dev@mcs.anl.gov</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;">I need to figure this out myself first.<br class="">In the meantime, here is another (PCASM related) question for you: why is PCASMType switched to BASIC when using a symmetric Pmat? (I guess I don’t have to tell you about the performance of RAS vs. ASM)<br class="">To me, that would make sense if the default KSP was also switched to CG instead of GMRES if the Pmat and Amat were symmetric, but I don’t think this is the case.<br class=""><br class="">Thanks,<br class="">Pierre<br class=""><br class="">> On 24 Oct 2019, at 5:40 PM, Smith, Barry F. <<a href="mailto:bsmith@mcs.anl.gov" target="_blank" class="">bsmith@mcs.anl.gov</a>> wrote:<br class="">><span class="Apple-converted-space"> </span><br class="">><span class="Apple-converted-space"> </span><br class="">> Send the code and exact instructions to run a "good" and a "bad" ASM<span class="Apple-converted-space"> </span><br class="">><span class="Apple-converted-space"> </span><br class="">> Barry<br class="">><span class="Apple-converted-space"> </span><br class="">><span class="Apple-converted-space"> </span><br class="">>> On Oct 14, 2019, at 10:44 AM, Pierre Jolivet <<a href="mailto:pierre.jolivet@enseeiht.fr" target="_blank" class="">pierre.jolivet@enseeiht.fr</a>> wrote:<br class="">>><span class="Apple-converted-space"> </span><br class="">>> Here are the three logs.<br class="">>> FGMRES also gives a wrong first iterate.<br class="">>> I think Mark was right in the sense that the problem is _most likely_ in my RHS.<br class="">>> But I need to figure out why I only get this problem with right-preconditioned KSPs with restrict or none.<br class="">>><span class="Apple-converted-space"> </span><br class="">>> Thanks,<br class="">>> Pierre<br class="">>><span class="Apple-converted-space"> </span><br class="">>><span class="Apple-converted-space"> </span><br class="">>><span class="Apple-converted-space"> </span><br class="">>>> On 13 Oct 2019, at 8:16 PM, Smith, Barry F. <<a href="mailto:bsmith@mcs.anl.gov" target="_blank" class="">bsmith@mcs.anl.gov</a>> wrote:<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Is this one process with one subdomain? (And hence no meaningful overlap since there is nothing to overlap?) And you expect to get the "exact" answer on one iteration?<span class="Apple-converted-space"> </span><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Please run the right preconditioned GMRES with -pc_asm_type [restrict and basic and none] -ksp_monitor_true_solution and send the output for the three cases.<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> For kicks you can also try FGMRES (which always uses right preconditioning) to see if the same problem appears.<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>> Barry<br class="">>>><span class="Apple-converted-space"> </span><br class="">>>><span class="Apple-converted-space"> </span><br class="">>>>> On Oct 13, 2019, at 2:41 AM, Pierre Jolivet via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov" target="_blank" class="">petsc-dev@mcs.anl.gov</a>> wrote:<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>> Hello,<br class="">>>>> I’m struggling to understand the following weirdness with PCASM with exact subdomain solvers.<br class="">>>>> I’m dealing with a very simple Poisson problem with Dirichlet + Neumann BCs.<br class="">>>>> If I use PCBJACOBI + KSPPREONLY or 1 iteration of GMRES either preconditioned on the right or on the left, I get the expected result, cf. attached screenshot.<br class="">>>>> If I use PCASM + KSPPREONLY or 1 iteration of GMRES preconditioned on the left, I get the expected result as well.<br class="">>>>> However, with PCASM + 1 iteration of GMRES preconditioned on the right, I don’t get what I should (I believe).<br class="">>>>> Furthermore, this problem is specific to -pc_asm_type restrict,none (I get the expected result with basic,interpolate).<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>> Any hint?<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>> Thanks,<br class="">>>>> Pierre<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type bjacobi -ksp_pc_side right -> bjacobi_OK<br class="">>>>> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type asm -ksp_pc_side left -> asm_OK<br class="">>>>> $ -sub_pc_type lu -ksp_max_it 1 -ksp_type gmres -pc_type asm -ksp_pc_side right -> asm_KO<br class="">>>>><span class="Apple-converted-space"> </span><br class="">>>>> <bjacobi_OK.png><asm_OK.png><asm_KO.png><br class="">>>><span class="Apple-converted-space"> </span><br class="">>><span class="Apple-converted-space"> </span><br class="">>> <dump-basic><dump-none><dump-restrict><br class="">><span class="Apple-converted-space"> </span><br class=""><br class=""></blockquote></div></div></blockquote></div><br class=""></div></blockquote></div><br clear="all" class=""><div class=""><br class=""></div>--<span class="Apple-converted-space"> </span><br class=""><div dir="ltr" class="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class="">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">-- Norbert Wiener</div><div class=""><br class=""></div><div class=""><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a></div></div></div></div></div></div></div></div></div></blockquote></div><br class=""></body></html>