On Fri, 16 Sep 2016 21:20:59 -0500, Joel C. Ewing  wrote:

>On 09/16/2016 12:44 AM, Bill Woodger wrote:
>> I had been wondering why there were not "rules of algebra" explanations for 
>> the floating-point variants of MULTIPLY. So I looked:
>>
>> "The sign of the product, if the product is numeric, is the exclusive or of 
>> the operand signs. This includes the sign of a zero or infinite product."
>>
>> In mathematics, is there a problem with infinity having a sign? Drifting OT 
>> again...
>>
>>
>Mathematically, discussing both +∞  and -∞ make sense, and they derive
>naturally in a number of contexts; such  as from considering the limit
>of  (1/x) as x→0 from the right (x>0) versus as x→0 from the left (x<0),
>or from just trying to describe both upper and lower bounds for real or
>natural numbers.
>
I agree.  There's also the notion of the affine model in which they're
different and the projective model in which they're the same.  See:

    https://en.wikipedia.org/wiki/Line_at_infinity#Geometric_formulation

Also:

    https://en.wikipedia.org/wiki/NaN#Encoding

TMI

-- gil

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