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

Charles R Harris charlesr.harris@gmail....
Mon Sep 29 17:54:31 CDT 2008


On Mon, Sep 29, 2008 at 4:40 PM, Charles R Harris <charlesr.harris@gmail.com
> wrote:

>
>
> 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
>

I also propose that all logical operators involving nan return false, i.e.,
==, !=, <, <=, >, >=, and, or, xor, not.
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