[petsc-users] DIVERGED_DTOL

[Jed Brown]

On Tue, Jan 8, 2013 at 11:08 AM, w_ang_temp <w_ang_temp at 163.com> wrote:

> 354 KSP preconditioned resid norm 2.882557881065e-01 true resid norm
> 3.089426814670e+04 ||r(i)||/||b|| 4.601523777979e-01
>

^^ Notice how this ratio is less than 1.0? DTOL is defined in terms of the
smallest residual norm seen.


> 355 KSP preconditioned resid norm 2.170676916299e+02 true resid norm
> 2.326457175403e+07 ||r(i)||/||b|| 3.465124326697e+02
> 356 KSP preconditioned resid norm 5.764266225925e+00 true resid norm
> 6.177943120636e+05 ||r(i)||/||b|| 9.20169 1405543e+00
> 357 KSP preconditioned resid norm 1.701448294063e+04 true resid norm
> 1.823554008687e+09 ||r(i)||/||b|| 2.716078947576e+04
>
> Linear solve did not converge due to DIVERGED_DTOL iterations 357
>
> I cannot understand it. Which one means that the DIVERGED_DTOL
> occures:preconditioned resid norm, true resid norm or ||r(i)||/||b||?
> What is the difference between preconditioned resid norm  and true resid
> norm?
>

It uses the norm that your method is running. In this case, it's the
preconditioned norm.
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