[petsc-users] MatGetRowMinAbs returns negative number

[Matthew Knepley]

On Thu, Jan 5, 2012 at 4:07 AM, Dominik Szczerba <dominik at itis.ethz.ch>wrote:

> Is it also possible that MaxAbs would be computed wrongly? I get a
> different value when I compute it myself.


Yes, that is possible. Here is the code:


http://petsc.cs.iit.edu/petsc/petsc-dev/annotate/d1799f05bf01/src/mat/impls/aij/seq/aij.c#l2628

    Matt


>
> Dominik
>
> On Thu, Jan 5, 2012 at 1:02 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> > On Jan 4, 2012, at 5:42 PM, Matthew Knepley wrote:
> >
> >> On Wed, Jan 4, 2012 at 5:29 PM, Dominik Szczerba <dominik at itis.ethz.ch>
> wrote:
> >> Do you think this issue can potentially explain a behavior I observe:
> >>
> >> In my big block shell matrix there are two blocks submatrices: (say) B
> >> and B transposed. MaxAbs is exact same for both submatrices, MinAbs is
> >> zero for B (as expected), but small negative for the other
> >> (unexpected).
> >>
> >> Now question: do I have a bug (that I do not immediately see) or this
> >> can be hopefully only a trick in MinAbs?
> >>
> >> It was a bug in MinAbs. I am pushing the fix.
> >
> >    To 3.2 I hope. Please send the patch link for 3.2 as Satish did just
> a little while ago for another bug.
> >
> >   Barry
> >
> >>
> >>    Matt
> >>
> >> Thanks a lot.
> >>
> >> On Wed, Jan 4, 2012 at 6:05 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> >> > On Wed, Jan 4, 2012 at 11:02, Matthew Knepley <knepley at gmail.com>
> wrote:
> >> >>
> >> >> Okay, here is what is wrong with the logic:
> >> >>
> >> >> 1) Its not a shift, it ignores values < 1.0e-12
> >> >
> >> >
> >> > you wrote that in the commit message
> >> >
> >> >>
> >> >>
> >> >> 2) The problem is on line 2.17 of the diff where it takes the first
> value
> >> >> as minimum, but does not take the absolute value
> >> >
> >> >
> >> > good catch
> >>
> >>
> >>
> >> --
> >> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> >> -- Norbert Wiener
> >
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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