[petsc-users] KSPMonitorSingularValue

[Richard Tran Mills]

I noticed this thread and just wanted to point out that you need to be 
careful with what you use these singular values for.  In my own 
(limited) experience, I seem to recall finding that the singular values 
you get from the Hessenberg matrix in GMRES are pretty inaccurate.  Your 
mileage may vary.

--Richard

On 10/20/2011 10:38 AM, Jed Brown wrote:
> On Thu, Oct 20, 2011 at 09:34, Klaij, Christiaan <C.Klaij at marin.nl 
> <mailto:C.Klaij at marin.nl>> wrote:
>
>     call
>     KSPMonitorSet(ksp,KSPMonitorSingularValue,PETSC_NULL,PETSC_NULL,ierr);
>
>
> This gets KSPMonitorSingularValue called after each iteration. That 
> routine prints the singular values.
>
>     call KSPSetComputeSingularValues(ksp,PETSC_TRUE,ierr)
>
>
> This instructs the KSP to save the extra information needed by the 
> monitor above.
>
>
>     in the part where I initialize the KSP. But where to call
>     KSPMonitorSingularValue? And how do I get "n" and "rnorm"?
>
>
> Do you want a monitor or do you want to extract estimates of the 
> singular values after KSPSolve has converged? You might be interested 
> in KSPComputeExtremeSingularValues(), for example.

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