[petsc-users] Stop KSP if diverging

[Smith, Barry F.]

   You most definitely want to call KSPGetConvergedReason() after every solve

    KSPConvergedReason reason
    ....

      call KSPSolve(ksp,b,x,ierr)
      call KSPGetConvergedReason(ksp,reason,ierr)
      if (reason .lt. 0) then
        printf*,'KSPSolve() has not converged'
        return
      endif


> On May 30, 2019, at 5:13 AM, Edoardo alinovi <edoardo.alinovi at gmail.com> wrote:
> 
> Hello Barry,
> 
> I am solving ns eqs using the standard simple algorithm.
> 
> As example let's say the the u velocity compoment diverges, the output of ksp is a nan as solution vector, but the program keeps going ahead solving also for the other components and for the pressure where again I get NaN. The only way to stop it is by hand using ctrl+C.
> 
> I am not using kspConvergedReason, maybe can you provide me an example in fortran?
> 
> Many thanks as always! 
> 
> On Wed, 29 May 2019, 23:54 Smith, Barry F., <bsmith at mcs.anl.gov> wrote:
> 
> 
> > On May 29, 2019, at 2:54 PM, Edoardo alinovi <edoardo.alinovi at gmail.com> wrote:
> > 
> > Hello Barry,
> > 
> > Using Matt's fix KSP stops exactly at the first NaN. Otherwise the simulation continues
> 
>    Yes, but what do you mean by the simulation? Are you calling KSPGetConvergedReason() after each solve to check if it was valid? Is the particular linear solver continuing to run with Nan? 
> 
> 
> 
> > even if everything is a NaN. I am using version 3.10.4, is this not enough up to date maybe? 
> > 
> > Tomorrow, I will run the monitor and get back to you. For today I have got my  "safe working limit"  :)
> > 
> > Thanks a lot guys for the help!
> > 
> > ------
> > 
> > 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
> > Website: https://www.edoardoalinovi.com/
> > 
> > 
> > 
> > 
> > Il giorno mer 29 mag 2019 alle ore 20:22 Smith, Barry F. <bsmith at mcs.anl.gov> ha scritto:
> > 
> >    Hmm, in the lastest couple of releases of PETSc the KSPSolve is suppose to end as soon as it hits a NaN or Infinity. Is that not happening for you? If you run with -ksp_monitor does it print multiple lines with Nan or Inf? If so please send use the -ksp_view output so we can track down which solver is not correctly handling the Nan or Info.
> > 
> >   That said if you call KSPSolve() multiple times in a loop or from SNESSolve() each new solve may have Nan or Inf (from the previous) but it should only do one iteration before exiting.
> > 
> >    You should always call KSPGetConvergedReason() after KSPSolve() and confirm that the reason is positive, if it is native it indicates something failed in the solve.
> > 
> >    Barry
> > 
> > 
> > > On May 29, 2019, at 2:06 AM, Edoardo alinovi via petsc-users <petsc-users at mcs.anl.gov> wrote:
> > > 
> > > Dear PETSc friends,
> > > 
> > > Hope you are doing all well.
> > > 
> > > I have a quick question for you that I am not able to solve by my self. Time to time, while testing new code features, it happens that KSP diverges but it does not stop automatically and the iterations continue even after getting a NaN. 
> > > 
> > > In the KSP setup I use the following instruction to set the divergence stopping criteria (div = 10000):
> > > 
> > > call KSPSetTolerances(myksp,  rel_tol,  abs_tol, div,  itmax,  ierr)
> > > 
> > > But is does not help. Looking into the documentation I have found also:
> > > KSPConvergedDefault(KSP ksp,PetscInt n,PetscReal rnorm,KSPConvergedReason *reason,void *ctx)
> > > Which I am not calling in the code. Is this maybe the reason of my problem? If yes how can I use KSPConvergedDefault in FORTRAN? 
> > > 
> > > Thanks,
> > > 
> > > Edo
> > > 
> > > ------
> > > 
> > > 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
> > > Website: https://www.edoardoalinovi.com/
> > > 
> > > 
> > 
>