On Jan 16, 2013, at 7:55 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
> At 2013-01-16 03:02:32,"Barry Smith" <bsmith at mcs.anl.gov> wrote:
> >
> >> 1.701448294063e+04 > 1.e4*1.145582415879e+00 hence it declares
> >> divergence
> Hello, Barry
> I made some tests and it is true. Thanks.
>
> But in the mannual, both version 3.2 and 3.3, the rule
> is:||rk||>dtol*||b||. It is ||b||, not r_0.
> My misunderstanding? Or the error in the manual?
Error in the manual. Depending on the solver it is either the preconditioned
norm or the unpreconditioned norm
> Besides, in the mannual, both version 3.2 and 3.3, the default dtol=1.0E+5.
> But from the results
> in the example, it is 1.0E+4.
Another error in the manual
> I donot know the reason. My petsc version is 3.2-p7.
None of this should really matter. The solver has gone bad at this point
regardless of specifics of how you measure it.
Barry
> Thanks. Jim
>
>
> >Note that at iteration 171 the preconditioned residual is 9.348832909193e-13
> >< 1.e-12 * 1.145582415879e+00 very good convergence.
> >
> >You seem to have set an unreasonably tight convergence criteria. In double
> >precision you can never realistically expect to use a rtol smaller than
> >e-12. In fact normally it is not reasonable to use more than like 1.e-8.
> >Those extra digits don't mean anything.
> >
> > Barry
> >
> >
>
>
