Please send -log_summary output with performance questions.<br><br><div class="gmail_quote">On Sun, Jul 22, 2012 at 4:01 AM, Bao Kai <span dir="ltr"><<a href="mailto:paeanball@gmail.com" target="_blank">paeanball@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi, Matt,<br>
<br>
I tried ML6.2 with petsc3.3 with default parameters by only specifying<br>
the preconditioner to be PCML. The KSP solver is gmres.<br>
<br>
The convergence rate is much faster, while it still took much longer<br>
time in total.<br>
<br>
For example, for the problem with 500^3 mesh ( 125 million unknowns )<br>
with 512nodes(4 processors per node) on bluegene/P , it tooks about<br>
ten iterations to get convergent while the total time used is about<br>
400 seconds.<br>
<br>
506 the KSP type is gmres<br>
507 the PC type is ml<br>
508 KSP rtol = 0.100000000000000008E-04 abstol =<br>
0.100000000000000001E-49 dtol = 10000.0000000000000 maxit = 10000<br>
509 SNES rtol = 0.100000000000000002E-07 abstol =<br>
0.100000000000000001E-49 stol = 0.100000000000000002E-07 maxit =<br>
50 maxf= 10000<br>
510 0 SNES Function norm 5.859593121800e+02<br>
511 0 KSP Residual norm 8.340827070202e+06<br>
512 1 KSP Residual norm 7.980806572332e+05<br>
513 2 KSP Residual norm 1.870896731234e+05<br>
514 3 KSP Residual norm 6.790580947452e+04<br>
515 4 KSP Residual norm 2.665552335248e+04<br>
516 5 KSP Residual norm 1.130212349885e+04<br>
517 6 KSP Residual norm 4.053599972292e+03<br>
518 7 KSP Residual norm 1.786770710693e+03<br>
519 8 KSP Residual norm 7.313571654931e+02<br>
520 9 KSP Residual norm 3.205683714450e+02<br>
521 10 KSP Residual norm 1.263243312734e+02<br>
522 11 KSP Residual norm 3.945082815178e+01<br>
523 1 SNES Function norm 9.378772067642e-02<br>
524 0 KSP Residual norm 5.413489711800e+01<br>
525 1 KSP Residual norm 1.442598710609e+01<br>
526 2 KSP Residual norm 4.073537172140e+00<br>
527 3 KSP Residual norm 1.157455598705e+00<br>
528 4 KSP Residual norm 3.509855901968e-01<br>
529 5 KSP Residual norm 1.160625342728e-01<br>
530 6 KSP Residual norm 3.209351890216e-02<br>
531 7 KSP Residual norm 7.780869881329e-03<br>
532 8 KSP Residual norm 1.820828886636e-03<br>
533 9 KSP Residual norm 4.172544590190e-04<br>
534 2 SNES Function norm 6.747963806680e-07<br>
535 Number of KSP iteration is 9<br>
536 SNES solve takes time 406.724867261176314<br>
<br>
But with bcgs and bjacobi, it tooks about 550 KSP iterations ( 2 snes<br>
iterations ) and 69 seconds to get the result.<br>
<br>
For much smaller problems, benefiting from the fast convergence, it<br>
did takes less time to get the result. It seems that the ml can not be<br>
scaled, or I used it in a wrong way.<br>
<br>
Best Regards,<br>
Kai<br>
<br>
<br>
> Message: 2<br>
> Date: Sat, 21 Jul 2012 08:47:10 -0500<br>
> From: Matthew Knepley <<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>><br>
> To: PETSc users list <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>><br>
> Subject: Re: [petsc-users] How to investigate the reason for slow<br>
> convergence rate?<br>
> Message-ID:<br>
> <<a href="mailto:CAMYG4GkfV6kmTFEKXUadOv%2B2CrKHk9hRY7UR-cFWf%2BvcRxCv5g@mail.gmail.com">CAMYG4GkfV6kmTFEKXUadOv+2CrKHk9hRY7UR-cFWf+vcRxCv5g@mail.gmail.com</a>><br>
> Content-Type: text/plain; charset="iso-8859-1"<br>
><br>
> On Sat, Jul 21, 2012 at 4:30 AM, Bao Kai <<a href="mailto:paeanball@gmail.com">paeanball@gmail.com</a>> wrote:<br>
><br>
>><br>
>>> HI, all,<br>
>><br>
>> I am still suffering from the slow convergence rate of the KSP solution.<br>
>><br>
>> I changed the code to use Petsc3.3 and then try the gamg precoditioner,<br>
>> the convergence rate is better, while it took more total time because it<br>
>> took much more time for each iteration and some extra time for<br>
>> pre-processing.<br>
>><br>
><br>
> Try ML to see if it has better defaults for your problem. If not, you will<br>
> have to start experimenting with the solver<br>
> parameters.<br>
><br>
><br>
>> I am wondering if there are some ways that can help me to investigate the<br>
>> slow convergence rate for KSP solution so that I can do some improvement.<br>
>> Is DMMG will be a good solution?<br>
>><br>
><br>
> No.<br>
><br>
> Matt<br>
><br>
><br>
>> Thank you very much.<br>
>><br>
>> Best Regards,<br>
>> Kai<br>
>><br>
>>><br>
>>> Message: 2<br>
>>> Date: Wed, 11 Jul 2012 15:17:15 -0500<br>
>>> From: Matthew Knepley <<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>><br>
>>> To: PETSc users list <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>><br>
>>> Subject: Re: [petsc-users] Does this mean the matrix is<br>
>>> ill-conditioned?<br>
>>> Message-ID:<br>
>>> <CAMYG4Gk7T=<br>
>>> <a href="mailto:q%2Bw1PKO7G_TW07iDzux90Sncbv9K7d0FD-MDrLRg@mail.gmail.com">q+w1PKO7G_TW07iDzux90Sncbv9K7d0FD-MDrLRg@mail.gmail.com</a>><br>
>>> Content-Type: text/plain; charset="iso-8859-1"<br>
>>><br>
>>> On Wed, Jul 11, 2012 at 12:40 PM, Bao Kai <<a href="mailto:paeanball@gmail.com">paeanball@gmail.com</a>> wrote:<br>
>>><br>
>>> > Hi, all,<br>
>>> ><br>
>>> > The following is the output from the solution of a Poisson equation<br>
>>> > from Darcy's law.<br>
>>> ><br>
>>> > To compute the condition number of matrix, I did not use PC and use<br>
>>> > GMRES KSP to do the test.<br>
>>> ><br>
>>> > It seems like that the condition number keep increasing during the<br>
>>> > iterative solution. Does this mean the matrix is ill-conditioned?<br>
>>> ><br>
>>><br>
>>> Generally yes. Krylov methods take a long time to resolve the smallest<br>
>>> eigenvalues, so this approximation is not great.<br>
>>><br>
>>><br>
>>> > For this test, it did not achieve convergence with 10000 iterations.<br>
>>> ><br>
>>> > When I use BJOCABI PC and BICGSTAB KSP, it generally takes about 600<br>
>>> > times iteration to get the iteration convergent.<br>
>>> ><br>
>>> > Any suggestion for improving the convergence rate will be much<br>
>>> > appreciated. The solution of this equation has been the bottleneck of<br>
>>> > my code, it takes more than 90% of the total time.<br>
>>> ><br>
>>><br>
>>> Try ML or GAMG.<br>
>>><br>
>>> Matt<br>
>>><br>
>>><br>
>>> > Thank you very much.<br>
>>> ><br>
>>> > Best Regards,<br>
>>> > Kai<br>
>>> ><br>
>>><br>
>>><br>
>>><br>
><br>
<span class="HOEnZb"><font color="#888888">><br>
> --<br>
> What most experimenters take for granted before they begin their<br>
> experiments is infinitely more interesting than any results to which their<br>
> experiments lead.<br>
> -- Norbert Wiener<br>
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