[petsc-users] Projection preconditioner as PCMG

[Jed Brown]

On Fri, Mar 9, 2012 at 05:16, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>wrote:

> Dear,
>
> To my earlier querry:
>
> What if I want to approximate my all coarse matrices with any Krylov
> iteration ?
>
> reply:
> The methods on each level are independent, you can set them with
> -mg_coarse_ksp_type gmres -mg_levels_1_ksp_type cg -mg_levels_1_ksp_max_it
> 100 -mg_levels_2_ksp_type minres ...
>
> This command line option changes the ksp_type on both ksp_pre and ksp_post
> (pre and post smoothing) .
> Where as I need to fix the ksp_post_type as RICHARDSON to get my Prec = C
> + I - AC ;
>

Do you want this on every level or still just the finest?


>
> If adapt pre_smoother as follows :
>
> ierr = MGGetSmootherDown(pcmg,lev,&ksp_pre); CHKERRQ(ierr);
> ierr = KSPSetType(ksp_pre, KSPGMRES);CHKERRQ(ierr);
>
> Does ONLY setting pre_smoother as GMRES means that GMRES iterates on
> coarse matrix at level = lev ?
>

Yes, this will only affect the pre-smoother (so it will then go to the next
coarser grid, come back, and do a post-smoother). You may have to increase
the number of iterations. I strongly recommend configuring the solver using
the command line and checking that it is the method you intended by reading
the output of -ksp_view.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120309/58a61efd/attachment-0001.htm>