petsc-users Digest, Vol 11, Issue 17

Barry Smith bsmith at
Wed Nov 18 14:53:52 CST 2009

    This only gives the final residual norm as computed by the Krylov  
method; so depending on your options it may be a preconditioned  
residual norm.

    If you want the true residual norm then you should compute it via  
the formula || b - A*x|| in your Fortran code after the KSPSolve()


On Nov 18, 2009, at 2:21 PM, Matthew Knepley wrote:

>   Matt
> On Wed, Nov 18, 2009 at 2:19 PM, <hxie at> wrote:
> Hi,
> I want to output the true residual norm after calling KSPSolve in a  
> fortran program. I know there is a command option '- 
> ksp_final_residual', but I cannot do this using the PBS job  
> submission. What is the related fortran subroutine for this? Thanks  
> for your help.
> Bests,
> Hui
> -- 
> 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

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