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Re: -0 and +0

At this point, I will need to review all of
our motions;  perhaps someone can help
remind me.  I vaguely recall we decided
we would have only one 0, and not -0 and +0
in the standard.  (Of course, this would not
mean implementers could not use this 754 feature
in implementing 1788.)

Baker

On 04/24/2013 10:08 AM, Richard Fateman wrote:

On 4/24/2013 7:54 AM, Vincent Lefevre wrote:

On 2013-04-24 07:24:24 -0700, Richard Fateman wrote:

I am hoping that to the largest extent the use of the IEEE-754
infinities will be transparent to this distinction. I am perhaps
naively assuming this comes up only in circumstances in which one
computes 1/oo or 1/(-oo) and gets not-quite zero. Allowing the use
of -0 provides an opportunity to encode [-oo,0) as [-oo,-0].

 From what I've heard, this was done by some implementations and this
was the reason why sqrt(-0) was chosen to return -0. However I wonder
whether introducing some particular non-closed intervals would be
useful. And it would make the standard more complex.

I think the only interval endpoints that would signify open  would be +-oo and -0.
I agree that -0 introduces a non-uniformity, but it slightly simplifies the programming,
at least if 1/(-oo)  -> -0 automatically. The big advantage is that 1/(-0) comes out as -oo
rather than oo. That is, I think, a selling point. Having open/closed endpoints at
every real would be more complicated, yes..

  I assume that the use of -0 has been
discussed and rejected some time previously by 1788 committee.




Since there is no distinction between 0 and +0, there is no encoding
for (0,oo]. As for whether endponts at +-oo are denoted with [] or
(), --- I would be pleased if this turns out to be a matter of
printing protocol, and nothing else.

I agree.






--

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Ralph Baker Kearfott,   rbk@xxxxxxxxxxxxx   (337) 482-5346 (fax)
(337) 482-5270 (work)                     (337) 993-1827 (home)
URL: http://interval.louisiana.edu/kearfott.html
Department of Mathematics, University of Louisiana at Lafayette
(Room 217 Maxim D. Doucet Hall, 1403 Johnston Street)
Box 4-1010, Lafayette, LA 70504-1010, USA
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