[petsc-users] Help with KSPSetConvergenceTest

[Edoardo alinovi]

Hello guys,

Today I am about to write a custom convergence test for KSP doing the
following job:

- if the number of ksp iterations is less than a given threshold, iterate
until that threshold is met
- if the number of ksp iterations is bigger than the threshold, use the
standard convergence checks.

As far as I understood from the examples, this is the function I need to
use:

KSPSetConvergenceTest
<https://petsc.org/main/manualpages/KSP/KSPSetConvergenceTest/>(ksp,MyKSPConverged,0,PETSC_NULL_FUNCTION,ierr)

With MyKSPConverge a subroutine (I am in fortran) where my custom
checks are implemented.

Here is how I have coded  MyKSPConverged:
















*    subroutine MyKSPConverged(ksp,n,rnorm,flag,dummy,ierr)       KSP
            ksp       PetscErrorCode ierr       PetscInt n,dummy
KSPConvergedReason flag       PetscReal rnorm       if (n>1) then
   call KSPConvergedDefault(ksp, n, rnorm, flag, ierr)       else
   flag = 0       endif       ierr = 0    end subroutine
MyKSPConverged*

However I get this error:
[0]PETSC ERROR: KSPSolve has not converged, reason DIVERGED_DTOL
which I believe to be triggered by *KSPConvergedDefault. *This is odd,
as this simulation converge perfectly if I comment ou my dodgy
convergence test.

*Do you have any advice for me?*

*thank you! *
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