In J, the reciprocal of zero is infinity. Correspondingly, the reciprocal of negative zero is negative infinity. Ergo, the reciprocal of negative infinity is negative zero.
%0 _ %_ 0 %__ 0 % %_ NB. The two zeros look identical _ % %__ NB. But J knows their "signs" __ So, you can produce a negative zero by inverting negative infinity, and you can identify a negative zero by inverting it. If __=%x then x is negative zero (the only value whose reciprocal is negative infinity). -Dan Please excuse typos; composed on a handheld device. On Jan 16, 2013, at 7:49 AM, Raul Miller <rauldmil...@gmail.com> wrote: > I thought that J did not represent negative zero? > > Is it possible to trick J into revealing a negative zero? If so, does > it involve foreigns or is there some native calculations that lead > here? > > Thanks, > > -- > Raul > > On Wed, Jan 16, 2013 at 7:26 AM, Henry Rich <henryhr...@nc.rr.com> wrote: >> On my awaking, there was a whiff of sulfur in the air, and a greenish >> haze... and somehow in my mind the idea that that last program won't work, >> because of the possibility of negative zero. I'll stay relegated to imp >> status. >> >> Henry Rich >> >> >> On 1/15/2013 6:20 PM, Henry Rich wrote: >>> >>> Nah, that's not beyond impish. The devilish solution is to take the >>> bitwise OR of the matrix with its conjugate transpose (but that's easier >>> in assembler language than in J: >>> (23 b.&.(a.&i.)&.(2&(3!:5))&.+. +@|:)) >>> ). And you need to be sure that the zeros on the lower diagonal and >>> below are true zeros! >>> >>> Henry Rich >>> >>> On 1/15/2013 6:03 PM, km wrote: >>>> >>>> Oh, boy! (v1`v2) } y <--> (v1 y) } (v2 y) >>>> >>>> Brief and devilish, take care for your soul, Henry! >>>> >>>> --Kip >>>> >>>> Sent from my iPad >>>> >>>> >>>> On Jan 15, 2013, at 3:39 PM, Henry Rich <henryhr...@nc.rr.com> wrote: >>>> >>>>> hft =: 0&=`(,: +@|:)} >>>>> >>>>> Henry Rich >>>>> >>>>> On 1/15/2013 5:25 AM, km wrote: >>>>>> >>>>>> This is an easy one. A Hermitian matrix matches its conjugate >>>>>> transpose. Write a verb hft that creates a Hermitian matrix from a >>>>>> triangular one that has a real diagonal. >>>>>> >>>>>> ishermitian =: -: +@|: >>>>>> ]A =: 2 2 $ 1 2j3 0 4 >>>>>> 1 2j3 >>>>>> 0 4 >>>>>> ]B =: hft A >>>>>> 1 2j3 >>>>>> 2j_3 4 >>>>>> ishermitian A >>>>>> 0 >>>>>> ishermitian B >>>>>> 1 >>>>>> >>>>>> Kip Murray >>>>>> >>>>>> Sent from my iPad >>>>>> ---------------------------------------------------------------------- >>>>>> 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 >>> >> ---------------------------------------------------------------------- >> 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
