[petsc-dev] gurus what does this mean?

[Patrick Lacasse]

What is the first "-pc_type none" in your example?
Is it overridden by "-pc_type lu"?




2014-04-29 0:21 GMT-04:00 Barry Smith <bsmith at mcs.anl.gov>:

>
> ex10 -f0 ~/Datafiles/Matrices/Foad -ksp_type gmres -pc_type none
> -ksp_gmres_restart 2000 -ksp_plot_eigenvalues -draw_pause -1
>  -ksp_monitor_true_residual -ksp_rtol 1.e-6 -ksp_max_it 1990 -geometry
> 0,0,600,600 -draw_save -pc_type lu -ksp_rtol 1.e-12
> -pc_factor_mat_solver_package superlu
>   0 KSP preconditioned resid norm 1.752626139140e+05 true resid norm
> 1.860478790525e+07 ||r(i)||/||b|| 1.000000000000e+00
>   1 KSP preconditioned resid norm 3.174750685865e+04 true resid norm
> 1.816271753408e+07 ||r(i)||/||b|| 9.762388921916e-01
>   2 KSP preconditioned resid norm 5.903085310063e-07 true resid norm
> 1.783619436500e-05 ||r(i)||/||b|| 9.586884008478e-13
>
> superlu does lots of pivoting for stability. What does it mean that the
> first iteration barely affects the residual and then the second iteration
> wipes it out?
>
> Right precondition wipes out the residual on one iteration
>
> gmres_restart 2000 -ksp_plot_eigenvalues -draw_pause -1
>  -ksp_monitor_true_residual -ksp_rtol 1.e-6 -ksp_max_it 1990 -geometry
> 0,0,600,600 -draw_save -pc_type lu -ksp_rtol 1.e-12
> -pc_factor_mat_solver_package superlu -ksp_pc_side right
>   0 KSP unpreconditioned resid norm 1.860478790525e+07 true resid norm
> 1.860478790525e+07 ||r(i)||/||b|| 1.000000000000e+00
>   1 KSP unpreconditioned resid norm 2.559955879548e-07 true resid norm
> 2.505789584416e-07 ||r(i)||/||b|| 1.346852002386e-14
> Number of iterations =   1
> Residual norm 2.50579e-07
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20140429/8261fa3c/attachment.html>