[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.

+1

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

Chuck
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