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Thank you very much!<br>
I will make some tests and let you know how it goes.<br>
<br>
Michele<br>
<br>
<div class="moz-cite-prefix">On 09/23/2013 01:24 PM, Mark F. Adams
wrote:<br>
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Ah yes, I agree, geometric MG with Galerkin is worth trying.
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<div>On Sep 23, 2013, at 3:36 PM, Dave May <<a
moz-do-not-send="true"
href="mailto:dave.mayhem23@gmail.com">dave.mayhem23@gmail.com</a>>
wrote:</div>
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<div>Hey Michele,<br>
<br>
I think Galerkin MG, even with a jump in the coefficient
of 10^3, can be made more robust and faster for your
problem.<br>
</div>
I'd start by trying different smoothers. Try
cheby/(bjacobi or asm), or gmres/(bjacobi or asm). When
using cheby, make sure you ask for the spectrum estimate.<br>
Definitely do more than one application of KSP on each
level.<br>
<div><br>
<div>I don't think you should switch to AMG without
first trying more robust smoothers and profiling how
much time is spent in the coarse grid solve.<br>
</div>
<div>I solve similar problems (geometry and size of the
jump) in connection with variable visocsity stokes
problems on structured grids, and I'm yet to see a
case with AMG is more robust and or faster than
Galerkin MG.<br>
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<br>
<br>
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<div>Cheers,<br>
</div>
<div> Dave<br>
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<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On 23 September 2013 20:52, Mark
F. Adams <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:mfadams@lbl.gov" target="_blank">mfadams@lbl.gov</a>></span>
wrote:<br>
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<div class="im"><br>
>><br>
> The simulation does start with both phases and
the geometry is supposed to become more complex as
the simulation progresses.<br>
> But so far the run is stopped before there are
significant changes in the shape of the droplet.<br>
<br>
</div>
Humm, not sure why you are seeing degradation then.
I imagine the initial geometry is not grid aligned so
I'm not sure why you are seeing degradation in
convergence rate.<br>
<div class="im"><br>
> I can give a shot to AMG: which options would
you suggest to use.<br>
<br>
</div>
-pc_type gamg -pc_gamg_type agg -pc_gamg_agg_nsmooths
1<br>
<div class="im"><br>
> Also, how can I project out the constant from
the rhs? Thanks a lot!<br>
<br>
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<a moz-do-not-send="true"
href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNullSpace.html#KSPSetNullSpace"
target="_blank">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNullSpace.html#KSPSetNullSpace</a><br>
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