[petsc-users] MatGetRowMinAbs returns negative number

[Barry Smith]

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