[petsc-users] petsc-users Digest, Vol 35, Issue 32

[Jed Brown]

On Fri, Nov 11, 2011 at 05:31, Bao Kai <paeanball at gmail.com> wrote:

> The following is the result with the options you told me. The iteration
> has converged, while converged at a wrong solution, compared to the result
> from LU.
>
> tutorials]$ time ./ex78 -Ain A_phi -rhs rhs_phi -solu solu_phi -noshift
> -pc_type hypre -pc_hypre_type parasails -ksp_gmres_restart 600 -ksp_rtol
> 1e-7 -ksp_typ gmres -ksp_monitor_true_residual -ksp_converged_reason
>
>
>  Read matrix in ascii format ...
> m: 288399, n: 288399, nz: 4023176
>  read A completed
>  rowNumber[0] = 13
>  rowNumber[1] = 13
>  rowNumber[2] = 19
>  read A is complete !
>
>  Read rhs in ascii format ...
>
>  Read exact solution in ascii format ...
>   0 KSP preconditioned resid norm 1.311815748108e+00 true resid norm
> 3.838432566849e-03 ||r(i)||/||b|| 1.000000000000e+00
>   1 KSP preconditioned resid norm 5.507600629359e-01 true resid norm
> 1.878066463331e-03 ||r(i)||/||b|| 4.892795250727e-01
> [...]
>  54 KSP preconditioned resid norm 1.106994152625e-07 true resid norm
> 2.679208019541e-03 ||r(i)||/||b|| 6.979953334807e-01
> Linear solve converged due to CONVERGED_RTOL iterations 54
>

Look, the true residual increased. This usually means that the
preconditioner is singular or nearly so. This is not a surprised, sparse
approximate inverse rarely works in my experience.
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