-0 comes up as part of normal computation:
% _1e_100 * 1e_300
__
% _1e_100 * _1e_300
_
Bo, the very useful
http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
suggests than log(+0)=__, log(-0)=NaN, but this is a proposal only;
IEEE-754 does not define log.
Henry Rich
On 1/16/2013 9:58 PM, Dan Bron wrote:
Since the only way to "natively" generate _0 in J is through %__, is it
worthwhile to put a check in % for __ and remove checks elsewhere? (e.g. in
i. or -:)? Of course, _0 could be introduced from the outside, in memory
mapped file or something, but caveat emptor, etc.
-Dan
-----Original Message-----
From: programming-boun...@forums.jsoftware.com
[mailto:programming-boun...@forums.jsoftware.com] On Behalf Of Roger Hui
Sent: Wednesday, January 16, 2013 9:10 PM
To: Programming forum
Subject: Re: [Jprogramming] Hermitian from triangular
Among other things, _0 is a pain in the neck in the dyad i. with hashing.
Also louses up straightforward algorithms for the dyad -:!.0 .
On Wed, Jan 16, 2013 at 3:38 PM, Henry Rich <henryhr...@nc.rr.com> wrote:
Negative zero makes sense as a last vestige of gradual underflow; and
anyway, it's well-behaved: it looks like 0 except when you take the
log, reciprocal, or square root. In any normal computation, it goes
away. In contrast, NaN messes up anything it touches.
I think we've had negative 0 in J forever. If NaN is a data virus, -0
is a virus that has been inserted into our DNA.
Henry Rich
On 1/16/2013 4:45 PM, Raul Miller wrote:
On Wed, Jan 16, 2013 at 4:35 PM, Henry Rich <henryhr...@nc.rr.com> wrote:
Negative zero isn't a bug, it's a feature that numerical types,
especially William Kahan, wanted to get into IEEE-754 to help out
some things. I'm not expert enough to explain.
Something similar could be said about NaN.
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