On Fri, May 11, 2012 at 4:47 PM, Karthik Duraisamy <span dir="ltr"><<a href="mailto:dkarthik@stanford.edu" target="_blank">dkarthik@stanford.edu</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear all,<br>
<br>
I have been able to use AMG (using ML) for some of my problems and am looking to delve deeper into the workings of the algorithm to better understand how to use it for larger and more complex problems. Since my problems are hyperbolic and involve sharp gradients, I think there is a possibility that coarse level operators are not very stable in some problems. I see evidence of this because in many cases, I need to use lu or a very high k ilu(k) on coarser levels to keep the iterative solver from diverging.<br>
<br>
In this regard, I am wondering whether it is possible to obtain the coarse grid operators (or at the very least, the eigenstructure at these levels). Right now, I am doing the monitoring at the baseline level but I am looking for additional information.<br>
</blockquote><div><br></div><div>You can get the smoother</div><div><br></div><div> <a href="http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/PC/PCMGGetSmoother.html">http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/PC/PCMGGetSmoother.html</a></div>
<div><br></div><div>This has the operator, and you can use the Krylov eigen approximation. You should have complete control.</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Regards,<br>
Karthik.<br>
<br>
--<br>
<br>
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Karthik Duraisamy<br>
Assistant Professor (Consulting)<br>
Durand Building Rm 357<br>
Dept of Aeronautics and Astronautics<br>
Stanford University<br>
Stanford CA 94305<br>
<br>
Phone: <a href="tel:650-721-2835" value="+16507212835">650-721-2835</a><br>
Web: <a href="http://www.stanford.edu/~dkarthik" target="_blank">www.stanford.edu/~dkarthik</a><br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<br>