a question about tolerance

Ryan Yan vyan2000 at gmail.com
Tue Sep 15 17:35:38 CDT 2009

Hi Jed,
Thanks a lot, it works after switching to the right .

But can you say a little more about what happened in the first scenario, I
did not quite fellow you. Let's say, If I set -ksp_rtol 1e-2, what does this
mean in the left PC case. More specifically, which term will be considered
as a stop creteria for the KSP solve.


On Tue, Sep 15, 2009 at 6:27 PM, Jed Brown <jed at 59a2.org> wrote:

> Ryan Yan wrote:
> > How can I explain the relative tolerance is function correctly? as you
> can
> > see from the term ||Ae||/||Ax||, neither of my testruns seems to stop at
> the
> > right place(should be 10^(-2), 10^(-3) respectively).
> The ||Ae||/||Ax|| column is not the preconditioned norm.  You are using
> left-preconditioned GMRES (the default) which uses the preconditioned
> norm.  Use
>  -ksp_right_pc -ksp_norm_type unpreconditioned
> for the behavior you seem to expect.
> Jed
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