Henry, ^.%__ NB. this log(-0) is bad
__ it could have been __j1p1 __j3.14159 in order to indicate the negative sign of -0. - Bo >________________________________ > Fra: Henry Rich <henryhr...@nc.rr.com> >Til: programm...@jsoftware.com >Sendt: 11:29 torsdag den 17. januar 2013 >Emne: Re: [Jprogramming] Hermitian from triangular > >-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. >>>> >>>> ------------------------------**------------------------------** >>> ---------- >>> For information about J forums see >>> http://www.jsoftware.com/**forums.htm<http://www.jsoftware.com/forums. >>> htm> >>> >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> >---------------------------------------------------------------------- >For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
