PETSc convergence criteria

[Nguyen, Hung V ERDC-ITL-MS]

Barry and Matt,

Thank you for the info. I rerun and got the information I need. 

-Hung
-----Original Message-----
From: owner-petsc-users at mcs.anl.gov [mailto:owner-petsc-users at mcs.anl.gov] On
Behalf Of Barry Smith
Sent: Wednesday, August 27, 2008 1:52 PM
To: petsc-users at mcs.anl.gov
Subject: Re: PETSc convergence criteria


   Also run with -ksp_converged_reason to see why the KSP solver is stopping.
You can also run with -ksp_monitor_true_residual to see what is happening to
the preconditioned residual norm and nonpreconditioned residual norm during
the computation.

    Barry


On Aug 27, 2008, at 1:39 PM, Matthew Knepley wrote:

> You are using the preconditioned norm for the convergence test. You 
> can use
>
> KSPSetNormType(ksp,  KSP_NORM_UNPRECONDITIONED)
>
> However, this will not work for all KSP types.
>
>   Matt
>
> On Wed, Aug 27, 2008 at 1:23 PM, Nguyen, Hung V ERDC-ITL-MS 
> <Hung.V.Nguyen at usace.army.mil> wrote:
>> All,
>>
>> We run a test case with  -ksp_rtol 1.0e-15 and -ksp_max_it 50000.  
>> Then we
>> compute the infinity and 2 norms of |a * xsolution -b| and the 
>> results are below. Why are these values of norms in a range 10e-8 to 
>> 10e-10 while -ksp_rtol is set 1.0e-15? What is the PETSc convergence 
>> criteria for the matrix solver?
>>
>> Thank you in advance,
>>
>> -Hung
>>
>>> hvnguyen:jade20% aprun -n 16 ./fw -ksp_type cg -pc_type bjacobi 
>>> -ksp_rtol 1.0e-15 -ksp_max_it 50000
>>> Time in PETSc solver =   0.7661848068237305       sec
>>> Computed solution - 2 norm of the residual error =
>>> 1.0662412498046400E-008
>>> Computed solution - maximum residual error (infinity norm) =
>>>   5.2750692702829838E-010
>>> Number of Krylov iterations =          257
>>> Application 281373 resources: utime 0, stime 0
>>
>>
>
>
>
> --
> What most experimenters take for granted before they begin their 
> experiments is infinitely more interesting than any results to which 
> their experiments lead.
> -- Norbert Wiener
>