[Insight-developers] Bug in vnl_powell.cxx

[Luis Ibanez]

Hans,

Thanks a lot for posting this.

I'll run some tests tomorrow, to try to include this bug fix in the release.


BTW: Note that there is a redundant implementation of the Powell optimizer
in ITK...


     Luis


------------------------------------------------------------
On Thu, Oct 30, 2008 at 10:35 PM, Bill Lorensen <bill.lorensen at gmail.com>wrote:

> Hans,
>
> I wonder why our testing never caught this. Are you taking a path
> through the code that we are not testing?
>
> Luis, we should definitely include the fixes in the new release.
>
> Bill
>
> On Thu, Oct 30, 2008 at 8:50 PM, Hans Johnson <hans-johnson at uiowa.edu>
> wrote:
> > ITK Developers,
> >
> > I just wanted to follow up on my previous e-mail a bit.
> >
> > I just found a nasty bug in the vxl_powell.cxx optimizer.  I've done
> > extensive testing on it, and figured out how fix it.  This has given my
> > application great speed increase, and no longer segmentation faults
> > randomly.  The problem was that a variable was not explicitly being set,
> and
> > from time to time it would have a non-zero initial value.  If you are
> really
> > lucky then the default initialization is zero, and all is well; if you
> are
> > somewhat lucky, the random value does not affect the outcome too much,
> and
> > the method converges after a bunch of iterations, and occasionally you
> are
> > unlucky and the the initialization is too crazy big/small and the
> function
> > being minmized evaluates to nan or inf and all heck breaks loose.
> >
> > The least invasive way to avoid this bug is to initialize the variable
> > "bx=0" on lines 87 and 124 of vnl_powell.cxx.  As stated in my previous
> > message, this does work, but a little more work also removes two façade
> > functions adapt the deprecated vnl_brent class member functions into the
> > vnl_brent_minimizer class.
> >
> > Since this is so close to a release, I wanted to recommend the minimally
> > invasisve fix prior to version 3.10, and the 15 line patch after the
> > release.
> >
> > Let me know what you think.
> > Hans
> > _______________________________________________
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> > Insight-developers at itk.org
> > http://www.itk.org/mailman/listinfo/insight-developers
> >
> >
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