Put another way, in the abstract, &.% is an identity transformation and (f -: f&.%) a tautology. So negative zero is -0 is -&.% 0 (only J is wise to the first trick, but not the second, sneakier one).
-Dan Please excuse typos; composed on a handheld device. On Jan 16, 2013, at 8:31 AM, Dan Bron <j...@bron.us> wrote: > 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
