<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Sep 23, 2013, at 11:55 AM, Michele Rosso <<a href="mailto:mrosso@uci.edu">mrosso@uci.edu</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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Hi,<br>
<br>
<font face="Ubuntu">I am successfully using PETSc to solve a 3D
Poisson's equation with CG + MG </font>. Such equation arises
from a projection algorithm for a multiphase incompressible flow
simulation.<br>
I set up the solver <font face="Ubuntu">as I was suggested to do
in a previous thread</font> (title: "GAMG speed") and run a test
case (liquid droplet with surface tension falling under the effect
of gravity in a quiescent fluid). <br>
The solution of the Poisson Equation via multigrid is correct but it
becomes progressively slower and slower as the simulation progresses
(I am performing successive solves) due to an increase in the number
of iterations.<br>
Since the solution of the Poisson equation is mission-critical, I
need to speed it up as much as I can.<br>
Could you please help me out with this?<br>
<br></div></blockquote><div><br></div><div>Just to add, it is not unusual as structures develop in your simulation to see an increase in iterations. If you plot the material coefficients I suspect that you will see sharper structures developing in time. Can you look at this in some way or generate some statistics like (max) gradient of material coefficients or even just max & min coefficients?</div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">
I run the test case with the following options:
<br>
<br>
-pc_type mg -pc_mg_galerkin -pc_mg_levels 5 -mg_levels_ksp_type
richardson -mg_levels_ksp_max_it 1
<br>
-mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package
superlu_dist
<br>
-log_summary -ksp_view -ksp_monitor_true_residual -options_left
<br>
<br>
Please find the diagnostic for the final solve in the attached file
"final.txt'.
<br>
Thank you,
<br>
<br>
Michele<br>
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<span><final.txt></span></blockquote></div><br></body></html>