On Mon, Sep 29, 2008 at 9:02 PM, David Cournapeau <david@ar.media.kyoto-u.ac.jp> wrote:

Charles R Harris wrote:
>
> So the proposition is, sign, max, min return nan when any of the
> arguments is nan.

Note that internally, signbit (the C function) returns an integer.

That is the signature of the ufunc. It could be changed... I believe the actual signbit of nan is undefined but I suppose we could return -1 in the nan case. That would be a fairly typical error signal for integers.

>
> Complex numbers are more complicated because we first compare the real
> parts, then the imaginary. Arguably 1 > 0 + nan*1j.

Really ? Without thinking about the consequences, returning a NaN
complex would be what I expect, should we go the route comparison with
NaN returns a NaN.

Yeah, I'm headed that way also.

> 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

Did you take a look at:

http://projects.scipy.org/scipy/numpy/wiki/ProperNanHandling

Note that in my branch the current behavior is

In [11]: a = np.array([0, np.nan, -1])

In [12]: np.max(a)
Out[12]: nan

In [13]: np.min(a)
Out[13]: nan

This is consistent with regarding nans as propagating errors. I can merge my branch back into yours if you want to play with these things.

Chuck