Stephan Kramer <[email protected]> writes: > We have been having some problems with GAMG on petsc-dev (master) for > cases that worked fine on petsc 3.4. We're solving a Stokes equation > (just the velocity block) for a simple convection in a square box > (isoviscous). The problem only occurs if we supply a near null space > (via MatSetNearNullSpace) where we supply the usual (1,0) (0,1) and > (-y,x) (near) null space vectors. If we supply those, the smoother > complains that the diagonal of the A matrix at the first coarsened > level contains a zero. If I dump out the prolongator from the finest > to the first coarsened level it indeed contains a zero column at that > same index. We're pretty confident that the fine level A matrix is > correct (it solves fine with LU). I've briefly spoken to Matt about > this and he suggested trying to run with -pc_gamg_agg_nsmooths 0 (as > the default changed from 3.4 -> dev) but that didn't make any > difference, the dumped out prolongator still has zero columns, and it > crashes in the same way. Do you have any further suggestions what to > try and how to further debug this?
Do you set the block size? Can you reproduce by modifying src/ksp/ksp/examples/tutorials/ex49.c (plane strain elasticity)?
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