And my discussion of his original hft has nothing to do with his new algorithm using bit-wise or!
Kip Sent from my iPad On Jan 16, 2013, at 9:33 AM, Raul Miller <rauldmil...@gmail.com> wrote: > But = is tolerant, and 0 = %__ > > -- > Raul > > On Wed, Jan 16, 2013 at 10:28 AM, km <k...@math.uh.edu> wrote: >> Henry's >> >> hft =: 0&=`(,: +@|:)} >> >> tests each element of its argument A returning 1 or 0 depending on whether >> the element is 0 . He doesn't know where this A is coming from, maybe >> somebody else's file. If he is comparing the bit representations of his 0 >> and one of A's 0's the test may return 0 instead of 1, and then the wrong >> element of A ,: +@|: A is chosen to go into the result B . >> >> Kip Murray >> >> Sent from my iPad >> >> >> On Jan 16, 2013, at 7:53 AM, Raul Miller <rauldmil...@gmail.com> wrote: >> >>> Ok, this makes sense, given the underlying hardware. >>> >>> But, I am having trouble reasoning about how this could cause problems >>> fro Henry's implementation, since: >>> >>> 0 = % __ >>> 1 >>> >>> and >>> >>> % ::0:"0 j./~_*i:1 >>> 0 0 0 >>> 0 _ 0 >>> 0 0 0 >>> >>> 0j1 % __ >>> 0 >>> % 0j1 % __ >>> _ >>> 0j1 * % __ >>> 0 >>> % 0j1 * % __ >>> _ >>> >>> Is there some way of getting an imaginary negative zero? Or is the >>> issue simply the result of % on the result of Henry's code on a matrix >>> with a negative zero off the diagonal? (Are there any other ways for >>> this to be a problem?) >>> >>> Thanks, >>> >>> -- >>> Raul >>> >>> On Wed, 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 >> ---------------------------------------------------------------------- >> 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
