Thanks Elijah and Clifford, for pointing me to the correct docs for <.@:% and <.!.0 . I suppose z <.@:% 32 is the way to do it, but (x:z)%32 and z%32x also work.
Also the following surprised me at first, but makes sense now: <. 8796093022248.562 8796093022249 Greetings, Ben On Thu, 29 Jul 2021 at 21:18, Clifford Reiter <reit...@lafayette.edu> wrote: > I think that comparison tolerance is the surprise. > > z =: 281474976711954 > > datatype z > > integer > > datatype z%32 > > floating > ((z%32)-<.z%32)%z%32 > > _4.9738e_14 > > 9!:18 '' NB. comparison tolerance > > 5.68434e_14 > > <.!.0 z%32 > > 8796093022248 > > <.(x: z)%32 > > 8796093022248 > > > <.!.0 or <.@:% "work" but only kick the can a few bits down the road as > z%32 is floating. > > Safest it to use rationals or exact integers. > > On Thu, Jul 29, 2021 at 3:02 AM Elijah Stone <elro...@elronnd.net> wrote: > > > On Thu, 29 Jul 2021, Ben Gorte wrote: > > > > > After > > > > > > z =: 281474976711954 > > > > > > compare > > > > > > <.z%32 > > > 8796093022249 > > > and > > > > > > z <.@:% 32 > > > > > > 8796093022248 > > > > <.@:% is recognised as a special combination, see the wiki page: > > > > > https://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations#Integer_Operations > > > > I am not sure why that happens; it certainly seems incorrect. The libc > > 'floor' function does not exhibit the same behaviour. If precision is > > important, using rationals may be a temporary workaround. > > ---------------------------------------------------------------------- > > 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
