[petsc-users] Norm of RHS in BCGS

[Matthew Knepley]

On Tue, Mar 22, 2016 at 2:50 AM, Norihiro Watanabe <norihiro.w at gmail.com>
wrote:

> Hi,
>
> Is it correct that a norm of a preconditioned RHS vector is used to
> compute a relative error in BCGS?
>

Yes, but you can verify this using -ksp_view


> I'm testing BCGS + BoomerAMG. With "-info", PETSc says "initial right
> hand side norm" is 2.223619476717e+10 (see below) but an actual norm
> of the RHS I passed is 4.059007e-02. If yes, is there any way to get a
> norm of a preconditioned RHS?
>

Do you mean unpreconditioned? You can try


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNormType.html

or use

  -ksp_monitor_true_residual

  Thanks,

    Matt


> [0] KSPConvergedDefault(): Linear solver has converged. Residual norm
> 2.036064453512e-02 is less than relative tolerance 9.999999960042e-13
> times initial right hand side norm 2.223619476717e+10 at iteration 6
>
>
> Regards,
> Nori
>
> --
> Norihiro Watanabe
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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