[petsc-users] Ksp Initial residual norm

[Smith, Barry F.]

> On Feb 3, 2019, at 1:16 PM, Edoardo alinovi <edoardo.alinovi at gmail.com> wrote:
> 
> Thank you very much Barry for the suggestion. 
> 
> Unfortunately, I am using Fortran and not C++ . Do you have an equivalent trick in this case? :)

   You would need to provide this function as a C function (in its own little .c file) and then call it from your Fortran code. 

   Barry

   There is no way to access the data structure directly from Fortran.

> ------
> 
> 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
> 
> 
> 
> 
> 
> Il giorno dom 3 feb 2019 alle ore 20:03 Smith, Barry F. <bsmith at mcs.anl.gov> ha scritto:
> 
>    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
> > 
> > 
> > 
>