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

[Filippo Spiga]

  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