Hi Ravi, <div><br></div><div>I have been using BoomerAMG as a preconditioner joint with an iterative solver, e.g. GMRES of BiCGs for regular 3D CFD problems. </div><div>On the top of my head, I can not remember if I had the strong scaling tests done (I will look into it and let you know if you found any), but for the weak-scaling case, I definitely saw some scaling issues. </div>
<div>As the size of the system increases, the number of iterations does also increase (somewhat significantly for my test problem, i.e. incompressible N-S with complex geometry) which ultimately deteriorates the weak-scaling behaviors. </div>
<div><br></div><div>This is also reported in the reports given by the hypre team, cf. </div><div><a href="https://computation.llnl.gov/casc/linear_solvers/pubs/pmis_report.pdf">https://computation.llnl.gov/casc/linear_solvers/pubs/pmis_report.pdf</a></div>
<div><br></div><div>(cf. see Table 6.1 for the Stokes flow simulation results and scaling). </div><div><br></div><div>Also, inherited with the multigrid nature, there are always fine-tuning factors which are, unfortunately, problem dependent. </div>
<div><br></div><div>Good luck, </div><div>Mohamad</div><div><br></div><div><div class="gmail_quote">On Thu, Dec 15, 2011 at 8:23 AM, Ravi Kannan <span dir="ltr"><<a href="mailto:rxk@cfdrc.com">rxk@cfdrc.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple" style="word-wrap:break-word"><div><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Dear All,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></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).<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></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?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Thanks,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Ravi. <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></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""> <a href="mailto:petsc-dev-bounces@mcs.anl.gov" target="_blank">petsc-dev-bounces@mcs.anl.gov</a> [mailto:<a href="mailto:petsc-dev-bounces@mcs.anl.gov" target="_blank">petsc-dev-bounces@mcs.anl.gov</a>] <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<u></u><u></u></span></p>
</div></div><p class="MsoNormal"><u></u> <u></u></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 :-)<u></u><u></u></p><div><p class="MsoNormal">
<u></u> <u></u></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.<u></u><u></u></p>
</div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Bobby<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p><div><div><p class="MsoNormal">On Dec 14, 2011, at 10:45 PM, Jed Brown wrote:<u></u><u></u></p>
</div><p class="MsoNormal"><br><br><u></u><u></u></p><div><p class="MsoNormal">On Wed, Dec 14, 2011 at 19:40, Dmitry Karpeev <<a href="mailto:karpeev@mcs.anl.gov" target="_blank">karpeev@mcs.anl.gov</a>> wrote:<u></u><u></u></p>
<p class="MsoNormal">The trouble is that the constraints can get "eliminated" only when they become active. <u></u><u></u></p></div><p class="MsoNormal"><u></u> <u></u></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.<u></u><u></u></p>
</div></div><p class="MsoNormal"><u></u> <u></u></p></div></div></div></blockquote></div><br></div>