[petsc-users] Advice Being Sought

[Jed Brown]

David Scott <d.scott at ed.ac.uk> writes:

> I forgot to say that the program ran on 128 MPI processes with the 
> following arguments
>    -pc_type gamg -pc_gamg_agg_nsmooths 1 -ksp_rtol 0.0001

Your problem is singular, as can be seen here:

  -mg_coarse_pc_type svd -mg_coarse_pc_svd_monitor

    SVD: condition number 4.795499711084e+15, 0 of 643 singular values are (nearly) zero
    SVD: smallest singular values: 1.007601359796e-11 1.599999673167e+02 1.599999753343e+02 1.599999841127e+02 1.599999906466e+02
    SVD: largest singular values : 4.527760228588e+04 4.558254786213e+04 4.648975485549e+04 4.809775098939e+04 4.831952029788e+04

Additionally, it appears that your right hand side is inconsistent.  The
null space is not the constant so I would indict the discretization
becoming degenerate somewhere.