Thank you very much!
I will make some tests and let you know how it goes.
Michele
On 09/23/2013 01:24 PM, Mark F. Adams wrote:
Ah yes, I agree, geometric MG with Galerkin is worth trying.
On Sep 23, 2013, at 3:36 PM, Dave May <[email protected]
<mailto:[email protected]>> wrote:
Hey Michele,
I think Galerkin MG, even with a jump in the coefficient of 10^3, can
be made more robust and faster for your problem.
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.
Definitely do more than one application of KSP on each level.
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.
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.
Cheers,
Dave
On 23 September 2013 20:52, Mark F. Adams <[email protected]
<mailto:[email protected]>> wrote:
>>
> The simulation does start with both phases and the geometry is
supposed to become more complex as the simulation progresses.
> But so far the run is stopped before there are significant
changes in the shape of the droplet.
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.
> I can give a shot to AMG: which options would you suggest to use.
-pc_type gamg -pc_gamg_type agg -pc_gamg_agg_nsmooths 1
> Also, how can I project out the constant from the rhs? Thanks a
lot!
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNullSpace.html#KSPSetNullSpace
