How to set the ksp true residual tolerance on command line

[Barry Smith]

    This depends on the Krylov solver and if you are using left or  
right preconditioning.  With right preconditioning it always uses the  
true residual norm.
So you can do -ksp_type gmres -ksp_pc_right
Some methods we do not have implemented for right preconditioning,  
like CG, in that case you can use -ksp_type cg -ksp_norm_type  
unpreconditioned
For CG many people prefer the energy norm which you can access with - 
ksp_norm_type natural

-ksp_view should always show which it is using

    Barry

On Jul 28, 2009, at 8:15 PM, Ryan Yan wrote:

> Hi all,
> Is there any way to set a true residual tolerance on command line. - 
> ksp_atol is for preconditioned residual norm only.
>
> Thanks,
>
> Yan