[petsc-users] Question concerning ilu and bcgs

[Karl Rupp]

Hi,

 > I have a matrix system Ax = b, A is of type MatSeqAIJ or MatMPIAIJ,
> depending on the number of cores.
>
> I try to solve this problem by pc_type ilu and ksp_type bcgs, it does
> not converge. The options I specify are:
>
> -pc_type hypre -pc_hypre_type pilut -pc_hypre_pilut_maxiter 1000
> -pc_hypre_pilut_tol 1e-3 -ksp_type b\
>
> cgs -ksp_rtol 1e-10 -ksp_max_it 1000 -ksp_monitor_short
> -ksp_converged_reason
>
>
> The first a few lines of the output are:
>
>    0 KSP Residual norm 1404.62
>
>    1 KSP Residual norm 88.9068
>
>    2 KSP Residual norm 64.73
>
>    3 KSP Residual norm 71.0224
>
>    4 KSP Residual norm 69.5044
>
>    5 KSP Residual norm 455.458
>
>    6 KSP Residual norm 174.876
>
>    7 KSP Residual norm 183.031
>
>    8 KSP Residual norm 650.675
>
>    9 KSP Residual norm 79.2441
>
>   10 KSP Residual norm 84.1985
>
>
> This clearly indicates non-convergence.

please send the full output. Where does your matrix A come from (i.e. 
which problem are you trying to solve)? Is this a serial run? ILU may 
fail depending on the particular choice of tolerance, pivoting, etc., so 
we need more information to suggest better options. Does the default 
GMRES+ILU0 work?

Best regards,
Karli