[petsc-users] Problems with preconditioners, which one?

[Hong Zhang]

This confirms that your Jacobian is singular, thus none of linear
solvers would work.
You need fix your function formulation (i.e., original model)
and Jacobian evaluation.

Hong


On Tue, Aug 3, 2010 at 10:35 AM, Filippo Spiga
<filippo.spiga at disco.unimib.it> wrote:
>  Hi Hong,
>    using 1 processor and  these parameters:
>
> -log_summary -pc_type lu -snes_type ls -snes_max_it 100000 -snes_rtol 1.e-8
> -snes_atol 1.e-4 -snes_monitor -snes_monitor_solution
> -snes_monitor_true_residual true -snes_monitor_solution_update -snes_view
>
> produces this error
>
>  0 SNES Function norm 7.421625102155e-02
> [0|11:22:07]: unknown: MatLUFactorNumeric_SeqAIJ() line 668 in
> src/mat/impls/aij/seq/aijfact.c: Zero pivot row 1 value 0 tolerance
> 2.77778e-14 * rowsum 0.0277778
>
> Anyway, if I use "ilu" instead if "lu" SNES converges and the results is
> "reasonable" (*). But, if I well understood, it is not possible to use ILU
> using more than one processor...
>
> Cheers
>
> (*)
> Solution_computed = [
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 0.0000000000000000e+00
> 3.7156349997233107e-02
> 2.7984940757539362e-01
> 1.7704468685117958e-01
> 2.7984964478539093e-01
> 3.8521416335084396e-01
> 2.3436084771103685e-01
> 1.7702464718082261e-01
> 2.3435582721155149e-01
> 2.2028936911050551e-01
> 7.0392659462312190e-01
> 8.3483864004318586e-01
> 6.2136685999260521e-01
> 8.3483987578535479e-01
> 7.9245140231855016e-01
> 6.6647854925988304e-01
> 6.2137752252899703e-01
> 6.6646262901401532e-01
> 7.1376045502521746e-01
> ];
>
> real_Solution = [
> 0
> 0
> 0
> 0
> 0
> 0
> 0
> 0
> 0
> 1/3
> 1/3
> 1/3
> 1/3
> 1/3
> 1/3
> 1/3
> 1/3
> 1/3
> 2/3
> 2/3
> 2/3
> 2/3
> 2/3
> 2/3
> 2/3
> 2/3
> 2/3
> ];
>
> Hong Zhang ha scritto:
>>
>> Run your code sequentially with option '-pc_type lu'.
>> Does it still diverge?
>
> FS
>