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]> 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 > >
