[petsc-users] while solving the linear system with half billion unknowns on the super computer with 1020 cores, the preconditioner pcmg couldn't set up

[Fande Kong]

Hi all,

I want to try to solve a problem with half billion unknowns with
preconditioner pcmg (Of course, I have successfully provided the
interpolation matrix and the coarse matrix).  When the size of the unknowns
is 1e7 level, the solve work very well with 1020 cores on the super
computer. But when the size of the unknowns increases to 1e8 level, the
preconditioner setup stage break down. The following is my run script that
I use to set the solver and the preconditioner.

 -pc_type mg  -ksp_type fgmres  -pc_mg_levels 2 -pc_mg_cycle_type v
-pc_mg_type multiplicative  -mg_levels_1_ksp_type richardson
-mg_levels_1_ksp_max_it 1 -mg_levels_1_pc_type asm
-mg_levels_1_sub_ksp_type preonly -mg_levels_1_sub_pc_type ilu
-mg_levels_1_sub_pc_factor_levels 1
-mg_levels_1_sub_pc_factor_mat_ordering_type rcm -mg_coarse_ksp_type gmres
-mg_coarse_ksp_rtol 0.1  -mg_coarse_ksp_max_it 2 -mg_coarse_pc_type asm
-mg_coarse_sub_ksp_type preonly -mg_coarse_sub_pc_type ilu
-mg_coarse_sub_pc_factor_levels 1
-mg_coarse_sub_pc_factor_mat_ordering_type rcm -ksp_view

My question is weather the linear system with half billion unknowns is too
big to solve. Or are there some bugs in preconditioner pcmg?

-- 
Fande Kong
ShenZhen Institutes of Advanced Technology
Chinese Academy of Sciences
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