From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Wed, 21 Aug 2013 13:47:56 -0400
To: 9fans@9fans.net
Message-ID: <461015d88dcdc89a3697e2e1d01a926c@kw.quanstro.net>
In-Reply-To: <2FEB81A6-7D40-427D-BF9B-07D90872E307@bitblocks.com>
References: <04891ed00c35de2583c1da9a017dd7e2@hamnavoe.com>
	<c93098b57ad99db811eb93d220b25f46@kw.quanstro.net>
	<2FEB81A6-7D40-427D-BF9B-07D90872E307@bitblocks.com>
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Subject: Re: [9fans] comparisons with NaN
Topicbox-Message-UUID: 7348e44c-ead8-11e9-9d60-3106f5b1d025

On Wed Aug 21 13:43:54 EDT 2013, bakul@bitblocks.com wrote:
> On Aug 21, 2013, at 9:55 AM, erik quanstrom <quanstro@quanstro.net> wro=
te:
>=20
> > On Wed Aug 21 12:09:26 EDT 2013, 9fans@hamnavoe.com wrote:
> >>> at least in terms of passing floating point test suites
> >>> (like python's) the NaN issue doesn't come up
> >>=20
> >> Actually it was a test suite that revealed the NaN errors.
> >> I wouldn't think it's something anyone needs in normal
> >> day-to-day computation, but sometimes boxes must be ticked.
> >=20
> > :-)  it is hard to imagine how this is useful.  it's not like
> > =E2=88=91{i=E2=86=92=E2=88=9E}-0 is interesting.  at least =E2=88=8F{=
i=E2=86=92=E2=88=9E}-0 has an alternating
> > sign.  (so does it converge with no limit?)
> >=20
> > the difference i have seen is a situation like
> > 	atan2(-0, x)	=E2=89=A1 -=CF=80
> > 	atan2(+0, x)	=E2=89=A1 pi, =E2=88=80 x<0.
> >=20
> > any ideas on how this is useful?
>=20
>=20
> See comments by Stephen Canon in
> http://stackoverflow.com/questions/1565164/what-is-the-rationale-for-al=
l-comparisons-returning-false-for-ieee754-nan-values

i think you selected a different antecedent for "this" than
i did.  by "this" i ment to refer to -0.

- erik