[petsc-dev] Multigrid is confusing

Barry Smith bsmith at mcs.anl.gov
Wed May 23 14:26:59 CDT 2012 

  This looks good:

$ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 2 -mg_levels_pc_type sor
lid velocity = 100, prandtl # = 1, grashof # = 10000
  Linear solve converged due to CONVERGED_RTOL iterations 10
  Linear solve converged due to CONVERGED_RTOL iterations 7
  Linear solve converged due to CONVERGED_RTOL iterations 8
  Linear solve converged due to CONVERGED_RTOL iterations 8
  Linear solve converged due to CONVERGED_RTOL iterations 9
  Linear solve converged due to CONVERGED_RTOL iterations 9
  Linear solve converged due to CONVERGED_RTOL iterations 8
  Linear solve converged due to CONVERGED_RTOL iterations 8
  Linear solve converged due to CONVERGED_RTOL iterations 7
Number of SNES iterations = 9

   I assume it is independent of the number of levels of refinement?

  Note that you could use -pc_type eisenstat perhaps in this case instead. Might save lots of flops?  I've often wondered about doing Mark's favorite chebyshev smoother with Eisenstat, seems like it should be a good match.



   Barry


On May 23, 2012, at 11:48 AM, Jed Brown wrote:

> If ex19 is what matters...
> 
> $ base='mpiexec.hydra -n 4 ./ex19 -da_refine 3 -lidvelocity 100 -grashof 1e4 -pc_type mg -ksp_type fgmres -pc_mg_type full -ksp_converged_reason'
> $ $base
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 23
>   Linear solve converged due to CONVERGED_RTOL iterations 12
>   Linear solve converged due to CONVERGED_RTOL iterations 12
>   Linear solve converged due to CONVERGED_RTOL iterations 17
>   Linear solve converged due to CONVERGED_RTOL iterations 15
>   Linear solve converged due to CONVERGED_RTOL iterations 13
>   Linear solve converged due to CONVERGED_RTOL iterations 19
>   Linear solve converged due to CONVERGED_RTOL iterations 21
>   Linear solve converged due to CONVERGED_RTOL iterations 18
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 1 -mg_levels_pc_type pbjacobi
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 25
>   Linear solve converged due to CONVERGED_RTOL iterations 27
>   Linear solve converged due to CONVERGED_RTOL iterations 27
>   Linear solve converged due to CONVERGED_RTOL iterations 30
>   Linear solve converged due to CONVERGED_RTOL iterations 28
>   Linear solve converged due to CONVERGED_RTOL iterations 42
>   Linear solve converged due to CONVERGED_RTOL iterations 49
>   Linear solve converged due to CONVERGED_RTOL iterations 52
>   Linear solve converged due to CONVERGED_RTOL iterations 48
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 1 -mg_levels_pc_type sor
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 22
>   Linear solve converged due to CONVERGED_RTOL iterations 16
>   Linear solve converged due to CONVERGED_RTOL iterations 17
>   Linear solve converged due to CONVERGED_RTOL iterations 19
>   Linear solve converged due to CONVERGED_RTOL iterations 19
>   Linear solve converged due to CONVERGED_RTOL iterations 17
>   Linear solve converged due to CONVERGED_RTOL iterations 20
>   Linear solve converged due to CONVERGED_RTOL iterations 18
>   Linear solve converged due to CONVERGED_RTOL iterations 17
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 2 -mg_levels_pc_type pbjacobi
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 15
>   Linear solve converged due to CONVERGED_RTOL iterations 13
>   Linear solve converged due to CONVERGED_RTOL iterations 16
>   Linear solve converged due to CONVERGED_RTOL iterations 15
>   Linear solve converged due to CONVERGED_RTOL iterations 16
>   Linear solve converged due to CONVERGED_RTOL iterations 16
>   Linear solve converged due to CONVERGED_RTOL iterations 18
>   Linear solve converged due to CONVERGED_RTOL iterations 17
>   Linear solve converged due to CONVERGED_RTOL iterations 16
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 2 -mg_levels_pc_type sor
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 10
>   Linear solve converged due to CONVERGED_RTOL iterations 7
>   Linear solve converged due to CONVERGED_RTOL iterations 8
>   Linear solve converged due to CONVERGED_RTOL iterations 8
>   Linear solve converged due to CONVERGED_RTOL iterations 9
>   Linear solve converged due to CONVERGED_RTOL iterations 9
>   Linear solve converged due to CONVERGED_RTOL iterations 8
>   Linear solve converged due to CONVERGED_RTOL iterations 8
>   Linear solve converged due to CONVERGED_RTOL iterations 7
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 3 -mg_levels_pc_type pbjacobi
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 12
>   Linear solve converged due to CONVERGED_RTOL iterations 9
>   Linear solve converged due to CONVERGED_RTOL iterations 11
>   Linear solve converged due to CONVERGED_RTOL iterations 11
>   Linear solve converged due to CONVERGED_RTOL iterations 11
>   Linear solve converged due to CONVERGED_RTOL iterations 12
>   Linear solve converged due to CONVERGED_RTOL iterations 12
>   Linear solve converged due to CONVERGED_RTOL iterations 11
>   Linear solve converged due to CONVERGED_RTOL iterations 11
> Number of SNES iterations = 9
> $ $base -mg_levels_ksp_type chebyshev -mg_levels_ksp_chebyshev_estimate_eigenvalues 0.1,1.1 -mg_levels_ksp_max_it 3 -mg_levels_pc_type sor
> lid velocity = 100, prandtl # = 1, grashof # = 10000
>   Linear solve converged due to CONVERGED_RTOL iterations 9
>   Linear solve converged due to CONVERGED_RTOL iterations 6
>   Linear solve converged due to CONVERGED_RTOL iterations 6
>   Linear solve converged due to CONVERGED_RTOL iterations 7
>   Linear solve converged due to CONVERGED_RTOL iterations 7
>   Linear solve converged due to CONVERGED_RTOL iterations 6
>   Linear solve converged due to CONVERGED_RTOL iterations 7
>   Linear solve converged due to CONVERGED_RTOL iterations 6
>   Linear solve converged due to CONVERGED_RTOL iterations 6
> Number of SNES iterations = 9
>

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