[petsc-users] rtol meaning

[Danny Lathouwers - TNW]

Thanks for the clarification. Petsc saves me a lot of time not having to write the icc etc so i can live with these small issues very well. Petsc behaves as expected now.
Danny

Sent from my iPad

> On 29 mei 2014, at 22:04, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> 
> 
>  Danny,
> 
>   The manual pages are a little sloppy and inconsistent. By default it uses ||b|| or || preconditioned b|| as the starting point. At the bottom of the badly formatted page you’ll see "- - rnorm_0 is the two norm of the right hand side. When initial guess is non-zero you can call KSPDefaultConvergedSetUIRNorm() to use the norm of (b - A*(initial guess)) as the starting point for relative norm convergence testing."
> 
> Likely you want to call KSPDefaultConvergedSetUIRNorm if that is how you want to detect convergence.
> 
>   We’ll cleanup the manual pages, thanks for pointing out the confusion.
> 
>   Barry
> 
>  You can see the source code at http://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/interface/iterativ.c.html#KSPDefaultConverged and confirm that what Matt said is correct.
> 
> 
>> On May 29, 2014, at 2:49 PM, Danny Lathouwers - TNW <D.Lathouwers at tudelft.nl> wrote:
>> 
>> Thanks Matt for your quick response.
>> 
>> I got to believe that it was the relative ratio of the residual from the following petsc links:
>> 
>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetTolerances.html
>> and
>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPDefaultConverged.html#KSPDefaultConverged
>> 
>> Perhaps these pages are outdated?
>> 
>> Cheers,
>> Danny.
>