[petsc-users] Propagating a constant marker with AMG

Jed Brown jed at jedbrown.org
Tue Mar 31 15:47:12 CDT 2015

John Mousel <john.mousel at gmail.com> writes:

> If I recall correctly, GAMG has a somewhat high setup cost and this is a
> solver I'll only be using for one single solve. It's not a physical field,
> it's just a marker; 1 inside, 0 outside a surface described by a CAD file.
> This marker is being propagated into the volume of an octree volumetric
> grid. I'm just taking advantage of the fact that the solution of the
> Laplace equation with constant BC's is the constant.

Oh, I see.  Enforce your boundary conditions so that the problems on
each side decouple, then use -pc_gamg_agg_nsmooths 0 (unsmoothed
aggregation).  Profile and let us know if it's a bottleneck.
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