[petsc-dev] -mat_error_if_fpe?

[Dmitry Karpeyev]

Ah, sorry.  I guess I was confused: I missed the fact that
-ksp_error_if_not_converged turns on mat->erroriffpe.

On Tue, Jun 2, 2015 at 3:23 PM Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Jun 2, 2015, at 4:11 PM, Dmitry Karpeyev <karpeev at mcs.anl.gov> wrote:
> >
> > -ksp_error_if_not_converged will not return immediately (it's easy to
> generate cases that will generate a lot of nans before getting anywhere
> close to returning -- use a pmat full of zeros, for example;  it is
> actually a real use case (a MOOSE phasefield test) where -snes_mf_operator
> with a finite-differencing produces a zero pmat).
>
>     I am totally confused. The flag -ksp_error_if_not_converged  just
> turns on the MatSetErrorIfFPE() so how could having an option
> -mat_error_if_fpe which would just turn on MatSetErrorIfFPE() result in any
> different kind of behavior.
>
>     If MatLUFactorSymbolic/Numeric() is not obeying the MatSetErrorIfFPE()
> then that needs to be fixed.
>
>
> >  When the solver returns with KSP_DIVERGED_INFORNAN, it provides only
> indirect information about what went wrong.   At the same time
> MatCheckPivot_none() will give you the row and the tolerance that triggered
> the zero pivot detection.  Currently, however, that behavior is turned on
> only by erroriffpe with no easy way to toggle.  Maybe we need a separate,
> more descriptive flag to error out on a zero pivot?  I would expect that
> users are used to the old behavior and occasionally rely on it for finding
> zero pivots.  They will be perplexed by this newfound inability to turn it
> back on.
>
>    They are suppose to turn it on with -ksp_error_if_not_converged  does
> that not work? Send me an example or point me to an example where that does
> not work.
>
>   Barry
>
>
> > Of course, I only have a single data point right now :-)
> >
> > On Tue, Jun 2, 2015 at 2:58 PM Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> > > On Jun 2, 2015, at 3:29 PM, Dmitry Karpeyev <karpeev at mcs.anl.gov>
> wrote:
> > >
> > > Currently -pc_type lu will not detect a zero pivot (it will happily
> produce an Inf or a NaN) and the flag it checks whether to see whether
> > > to do it is erroriffpe.   KSP_DIVERGED_NANORINF is too generic.  What
> if the user wants to verify there is a zero pivot?
> >
> >
> >    -ksp_error_if_not_converged will cause an immediate stack trace when
> the zero pivot occurs (as would the user calling MatSetErrorIfFPE() on the
> matrix or the use of -mat_error_if_fpe if it existed).
> >
> >    There is no way currently to get back programatically anything more
> specific than KSP_DIVERGED_NANORINF on a zero pivot, we can start adding
> more that has nothing to do with -mat_error_if_fpe
> >
> > >
> > > Also, irrespective of the use case, if we have a XXXSetYYY(), isn't
> our policy to have a command-line way of doing it?
> >
> >   No, only when it makes sense and doesn't duplicate other
> functionality. I don't see -mat_error_if_fpe in this case adding anything
> more helpful then the already existing -ksp_error_if_not_converged
> >
> >   Convince me.
> >
> >   Barry
> >
> >
> >
> > >
> > > On Tue, Jun 2, 2015 at 2:21 PM Barry Smith <bsmith at mcs.anl.gov> wrote:
> > >
> > > > On Jun 2, 2015, at 3:02 PM, Dmitry Karpeyev <karpeev at mcs.anl.gov>
> wrote:
> > > >
> > > > Should we have a way to turn on/off MatErrorIfFPE() on the command
> line?
> > >
> > >   Sure, one does it with -ksp_error_if_not_converged or
> -snes_error_if_not_converged  It only adds to user confusion, but no user
> benefit, to have a -mat_error_if_fpe thing.
> > >
> > >   What user case do think there is for a -mat_error_if_fpe ?
> > >
> > >   Barry
> > >
> > >
> > >
> > > > It is now turned off by default to allow Inf/NaNs to propagate and
> currently the only way to toggle it is programmatic.
> > >
> > >
> > > >
> > > > Dmitry.
> > >
> >
>
>
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