[Numpy-discussion] What is the sign of nan?

Charles R Harris charlesr.harris@gmail....
Mon Sep 29 17:40:28 CDT 2008

On Mon, Sep 29, 2008 at 4:28 PM, Robert Kern <robert.kern@gmail.com> wrote:

> On Mon, Sep 29, 2008 at 17:13, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
> >
> > On Mon, Sep 29, 2008 at 3:52 PM, Charles R Harris
> > <charlesr.harris@gmail.com> wrote:
> >>
> >> Hi All,
> >>
> >> I've been cleaning up the ufunc loops and the sign function currently
> >> doesn't have a defined behavior for nans. This makes the results depend
> on
> >> the order/type of comparisons in the code, which looks fragile to me. So
> >> what should it return? I vote for nan but am open for suggestions.
> >
> > And while we're at it, lets decide how to treat max/min when nans are
> > involved. Or should we just say the behavior is undefined.
> When feasible, I would like float(s)->float functions to return NaN
> when given a NaN as an argument. At least as the main versions of the
> function. Specific NaN-ignoring functions can also be introduced, but
> as separate functions. I don't know what exactly to do about
> float->int functions (e.g. argmin). I also don't know how these should
> interact with the current seterr() state.

So the proposition is, sign, max, min return nan when any of the arguments
is nan.


Complex numbers are more complicated because we first compare the real
parts, then the imaginary. Arguably 1 > 0 + nan*1j. I propose that the sign
of a complex number containing nans should be nan, but I can't decide what
should happen with max/min

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