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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple style='word-wrap: break-word;-webkit-nbsp-mode: space;-webkit-line-break: after-white-space'><div class=WordSection1><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear All,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>This is Ravi Kannan from CFD Research Corporation. Recently, we are experimenting with the BoomerAMG preconditioner for some “stiff” CFD problems. In that regard, all the other standard solver-preconditioner combinations failed for the current CFD problem. The boomer is the only one which is able to provide with “converged” solutions.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>We noticed that the scalability of this boomer preconditioner is really poor. For instance, even with a cell size of 2 million, we cannot scale to even 16 partitions (in contrast, the other solver-preconditioner combinations like the BI-CGS/BJacobi gave good enough scalability).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Are we missing something? Do we need to use a more latest version of boomer?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Ravi. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> petsc-dev-bounces@mcs.anl.gov [mailto:petsc-dev-bounces@mcs.anl.gov] <b>On Behalf Of </b>Bobby Philip<br><b>Sent:</b> Thursday, December 15, 2011 9:22 AM<br><b>To:</b> For users of the development version of PETSc<br><b>Subject:</b> Re: [petsc-dev] controlling vector values while doing matrix free operations<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hmmmm..sorry guys - the entire thread got put away in a folder by my mail reader and I just discovered all your emails :-)<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>SNESVI looks interesting but as someone pointed out I am using matrix free. And as I understand from Barry a matrix free version of SNESVI is not implemented. The idea of flipping the sign seems to be a poor mans approach that might work for me though I would still need some mechanisms in SNES to put the hooks in.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Bobby<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Dec 14, 2011, at 10:45 PM, Jed Brown wrote:<o:p></o:p></p></div><p class=MsoNormal><br><br><o:p></o:p></p><div><p class=MsoNormal>On Wed, Dec 14, 2011 at 19:40, Dmitry Karpeev <<a href="mailto:karpeev@mcs.anl.gov">karpeev@mcs.anl.gov</a>> wrote:<o:p></o:p></p><p class=MsoNormal>The trouble is that the constraints can get "eliminated" only when they become active. <o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>That's not what I meant. I meant to transform the algebraic system so that those extra variables were eliminated. The point is that we tend to put a lot of effort into designing effective preconditioners for a standard formulation (e.g. conservative variables), and that is partly lost of we have this other system in which the evaluations of constitutive relations are added explicitly.<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>