[petsc-users] Richardson with direct solver does not converge in preconditioned residual norm

[Jed Brown]

Is this problem singular?

On Thu, Feb 2, 2012 at 13:47, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> For some tests I use richardson iterations with direct solver for
> preconditioning (if everything is fine, richardson should be replaces by
> preonly).
>
>  -ksp_type richardson -pc_type lu -pc_factor_mat_solver_package mumps
> -ksp_monitor -ksp_monitor_true_residual -ksp_max_it 10
>
> For some matrices I see that it converges fine in true residual norm but
> not in the preconditioned one:
>
>  0 KSP Residual norm 1.540366130785e+05
>  0 KSP preconditioned resid norm 1.540366130785e+05 true resid norm
> 4.257656834616e+04 ||r(i)||/||b|| 1.000000000000e+00
>  1 KSP Residual norm 1.355077212761e+05
>  1 KSP preconditioned resid norm 1.355077212761e+05 true resid norm
> 1.468758291284e-11 ||r(i)||/||b|| 3.449686877867e-16
>  2 KSP Residual norm 3.775360693480e+05
>  2 KSP preconditioned resid norm 3.775360693480e+05 true resid norm
> 5.008860262312e-12 ||r(i)||/||b|| 1.176435879376e-16
>  3 KSP Residual norm 1.714431257209e+05
>  3 KSP preconditioned resid norm 1.714431257209e+05 true resid norm
> 5.365631839419e-12 ||r(i)||/||b|| 1.260231166541e-16
>  4 KSP Residual norm 7.164219897555e+04
>  4 KSP preconditioned resid norm 7.164219897555e+04 true resid norm
> 5.582291603774e-12 ||r(i)||/||b|| 1.311118256030e-16
>  5 KSP Residual norm 2.480147180914e+05
>  5 KSP preconditioned resid norm 2.480147180914e+05 true resid norm
> 5.464714292269e-12 ||r(i)||/||b|| 1.283502758569e-16
>  6 KSP Residual norm 1.749548383255e+05
>  6 KSP preconditioned resid norm 1.749548383255e+05 true resid norm
> 6.601924132117e-12 ||r(i)||/||b|| 1.550600339239e-16
>  7 KSP Residual norm 1.873773824295e+05
>  7 KSP preconditioned resid norm 1.873773824295e+05 true resid norm
> 6.368611865551e-12 ||r(i)||/||b|| 1.495802060366e-16
>  8 KSP Residual norm 2.610223461339e+05
>  8 KSP preconditioned resid norm 2.610223461339e+05 true resid norm
> 8.365362648969e-12 ||r(i)||/||b|| 1.964780858090e-16
>  9 KSP Residual norm 2.459609758347e+05
>  9 KSP preconditioned resid norm 2.459609758347e+05 true resid norm
> 8.427381039077e-12 ||r(i)||/||b|| 1.979347177668e-16
>  10 KSP Residual norm 1.611793769272e+05
>  10 KSP preconditioned resid norm 1.611793769272e+05 true resid norm
> 8.325158481093e-12 ||r(i)||/||b|| 1.955338066095e-16
>
>
> Would could be the reason for?
>
> Thomas
>
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