Re: [9fans] comparisons with NaN

[erik quanstrom <quanstro@quanstro.net>]

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> wrote:
> 
> > 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
> >> 
> >> 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.
> > 
> > :-)  it is hard to imagine how this is useful.  it's not like
> > ∑{i→∞}-0 is interesting.  at least ∏{i→∞}-0 has an alternating
> > sign.  (so does it converge with no limit?)
> > 
> > the difference i have seen is a situation like
> > 	atan2(-0, x)	≡ -π
> > 	atan2(+0, x)	≡ pi, ∀ x<0.
> > 
> > any ideas on how this is useful?
> 
> 
> See comments by Stephen Canon in
> http://stackoverflow.com/questions/1565164/what-is-the-rationale-for-all-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