[petsc-users] KSP diverging

[Mohamad M. Nasr-Azadani]

Thank you guys,
What happens right now when I use GMRES is that it reaches the maximum
number of iterations I set, i.e. 1000 (which should not). I have set the
restart to 20 (and then increased it to 1000) but no luck. It never
converges.


On Fri, Dec 23, 2011 at 7:23 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Fri, Dec 23, 2011 at 07:43, Matthew Knepley <knepley at gmail.com> wrote:
>
>> Even if you lose orthogonality, it will just stagnate since you always
>> have the solution
>> from the first few vectors. Likewise, I do not see how you can get an
>> diverging sequence
>> from restarting since you always have the last residual, you just
>> stagnate.
>>
>
> The true residual can grow even though the estimate of the preconditioned
> residual decreases monotonically. When you restart, you re-evaluate the
> actual residual, which might be much larger.
>
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