[petsc-users] Suggestions for solver and pc

[Sal Am]

Hello,

So I am trying to solve this problem in the frequency domain by solving a
Ax=b. It is apparently very ill conditioned. RF wave plasma interaction
simulation. There are 6M finite elements the matrix is of the size:

nnx: 1257303210 (1B non-zero elements)
n: 20347817 (size of matrix so 20M x 20M)

*What I have tried so far: *

 -ksp_type bcgs -pc_type gamg

 -ksp_type gmres -ksp_gmres_restart 150 -pc_type bjacobi -sub_pc_type ilu
-sub_pc_factor_levels 5 -sub_ksp_type bcgs -mattransposematmult_via
scalable -build_twosided allreduce

-ksp_type bcgs -pc_type gamg -mattransposematmult_via scalable
-build_twosided allreduce

-ksp_type bcgs -pc_type asm -sub_pc_type lu

None of the above has really shown any convergence after 2 days of running
the simulation. The farthest I got was using gmres + bjacobi which gave me
a ||r||/||b|| of the order 1e-2 but it got stuck between 1e-2 and 1e-1
after a week of having left it running.


*What I have available in terms of computational resources:*
select=25:ncpus=16:mpiprocs=16:mem=230GB

So 25 nodes with around 6TB of total memory.

Thank you.
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