[Numpy-discussion] nan, sign, and all that
Charles R Harris
Thu Oct 2 08:22:28 CDT 2008
On Thu, Oct 2, 2008 at 1:42 AM, Robert Kern <email@example.com> wrote:
> On Thu, Oct 2, 2008 at 02:37, Stéfan van der Walt <firstname.lastname@example.org>
> > Hi Charles,
> > 2008/10/2 Charles R Harris <email@example.com>:
> >> In : a = array([NAN, 0, NAN, 1])
> >> In : b = array([0, NAN, NAN, 0])
> >> In : fmax(a,b)
> >> Out: array([ 0., 0., NaN, 1.])
> >> In : fmin(a,b)
> >> Out: array([ 0., 0., NaN, 0.])
> > These are great, many thanks!
> > My only gripe is that they have the same NaN-handling as amin and
> > friends, which I consider to be broken.
> No, these follow well-defined C99 semantics of the fmin() and fmax()
> functions in libm. If exactly one of the arguments is a NaN, the
> non-NaN argument is returned. This is *not* the current behavior of
> amin() et al., which just do naive comparisons.
> > Others also mentioned that
> > this should be changed, and I think David C wrote a patch for it (but
> > I am not informed as to the speed implications).
> > If I had to choose, this would be my preferred output:
> > In : fmax(a,b)
> > Out: array([ NaN, NaN, NaN, 1.])
> Chuck proposes letting minimum() and maximum() have that behavior.
Yes. If there is any agreement on this I would like to go ahead and do it.
It does change the current behavior of maximum and minimum.
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