[petsc-dev] handling user domain errors

[Dmitry Karpeyev]

Barry,
Sorry, I must have missed this -- I really ought to make a better filter
for catching email like this.
I think using NaNs is an excellent solution, in fact, I was proposing it a
few months ago here :-)
http://lists.mcs.anl.gov/pipermail/petsc-dev/2015-February/016958.html
It ensures that the error is collective (the norm reduction will ensure
every rank gets a NaN),
the "error condition" is cleared automatically on the next MatMult, etc.
I'm all for it.
Should I put it in?

Dmitry.

On Wed, Apr 29, 2015 at 8:26 PM Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Dmitry,
>
>     I haven't heard back from you on this. Any thoughts?
>
>   Barry
>
> > On Apr 20, 2015, at 6:23 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> >  Dmitry,
> >
> >   Rather than introducing another whole complexity of flags for
> indicating domain errors in user functions just do the following.
> >
> >   1) just stick a Nan into the functions result
> >   2) remove the VecValidValues() at the END of routines like MatMult()
> >   3) when Nan or Inf pop up in Krylov methods (which will happen within
> VecNorm or VecDot() and thus we get free collective knowledge of the
> problem even if it happened on only one node), generate the appropriate
> KSP_DIVERGED_NANORINF. This is already handled sometimes (most of the
> time?), for example in KSPSolve_CG is code
> > ierr = VecXDot(Z,R,&beta);CHKERRQ(ierr);         /*  beta <- z'*r
>  */
> >    if (PetscIsInfOrNanScalar(beta)) {
> >      if (ksp->errorifnotconverged)
> SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_NOT_CONVERGED,"KSPSolve
> has not converged due to Nan or Inf inner product");
> >      else {
> >        ksp->reason = KSP_DIVERGED_NANORINF;
> >        PetscFunctionReturn(0);
> >      }
> >    }
> >
> >   4) SNES already handles failed to converge KSP and
> >   5 ) TS already handles failed to converged SNES; by, for example,
> cutting the timestep.
> >
> >  Barry
> >
> >
>
>
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