[petsc-users] Ksp Initial residual norm

[Smith, Barry F.]

   If you use the default KSP convergence tests (which almost everyone does) the initial residual norm is stored in ksp->rnorm0. Thus to access it you need to include the private header file that defines the KSP object kspimpl.h so something like 

#include <petsc/private/kspimpl.h> 

   PetscErrorCode KSPGetInitialResidualNorm(KSP ksp,PetscReal *norm0)
  {
   *norm0 = ksp->rnorm0;
   return 0;
  }

should work.

   Barry




   

> On Feb 3, 2019, at 8:27 AM, Edoardo alinovi via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> Dear all,
> 
> I have a very simple question for you. How can I get the initial residual from a ksp solver? I can easily extract the final (preconditioned) residual norm  but  when I try to use to do the same with the initial residual using:
> 
> kspInitialResidual()
> 
> PETSc tells me that this feature is not supported. I am actually doing it applying the definition of residual "by hand", but I am wondering if somenthing already built-in is available or not. 
> 
> Thank you very much! 
> ------
> 
> Edoardo Alinovi, Ph.D.
> 
> DICCA, Scuola Politecnica,
> Universita' degli Studi di Genova,
> 1, via Montallegro,
> 16145 Genova, Italy
> 
> Email: edoardo.alinovi at dicca.unige.it
> Tel: +39 010 353 2540
> 
> 
>