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Mark,<br>
<br>
thank you for your input and sorry my late reply: I saw your email
only now.<br>
By setting up the solver each time step you mean re-defining the KSP
context every time? Why should this help?<br>
I will definitely try that as well as the hypre solution and report
back.<br>
Again, thank you.<br>
<br>
Michele<br>
<br>
<div class="moz-cite-prefix">On 05/22/2014 09:34 AM, Mark Adams
wrote:<br>
</div>
<blockquote
cite="mid:CADOhEh59U0gn1aZ3vPFs6mzb2FAnjAMcz8XuGCRAxf1hwE6xuQ@mail.gmail.com"
type="cite">
<div dir="ltr">If the solver is degrading as the coefficients
change, and I would assume get more nasty, you can try deleting
the solver at each time step. This will be about 2x more
expensive, because it does the setup each solve, but it might
fix your problem.
<div>
<br>
</div>
<div>You also might try:</div>
<div><br>
</div>
<div>
<div>-pc_type hypre</div>
<div>-pc_hypre_type boomeramg</div>
<div><br>
</div>
<div><br>
</div>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Mon, May 19, 2014 at 6:49 PM, Jed
Brown <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:jed@jedbrown.org" target="_blank">jed@jedbrown.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="">Michele Rosso <<a moz-do-not-send="true"
href="mailto:mrosso@uci.edu">mrosso@uci.edu</a>>
writes:<br>
<br>
> Jed,<br>
><br>
</div>
> thank you very much!<br>
> I will try with ///-mg_levels_ksp_type chebyshev
-mg_levels_pc_type<br>
> sor/ and report back.<br>
<div class="">> Yes, I removed the nullspace from both
the system matrix and the rhs.<br>
> Is there a way to have something similar to Dendy's
multigrid or the<br>
> deflated conjugate gradient method with PETSc?<br>
<br>
</div>
Dendy's MG needs geometry. The algorithm to produce the
interpolation<br>
operators is not terribly complicated so it could be done,
though DMDA<br>
support for cell-centered is a somewhat awkward. "Deflated
CG" can mean<br>
lots of things so you'll have to be more precise. (Most
everything in<br>
the "deflation" world has a clear analogue in the MG world,
but the<br>
deflation community doesn't have a precise language to talk
about their<br>
methods so you always have to read the paper carefully to
find out if<br>
it's completely standard or if there is something new.)<br>
</blockquote>
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<br>
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</blockquote>
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