How would a new user know that using mod with large numbers was 'asking the wrong question'?
Surely user-friendly code protects the user as its first priority? Regards, Rob. > On 7 Sep 2017, at 14:24, Eric Iverson <eric.b.iver...@gmail.com> wrote: > > Rob, > > To get your right answer, you have to ask the right question. It seems in > your case the right question has x: and for others the right question does > not. > >> On Thu, Sep 7, 2017 at 9:17 AM, Rob B <rb75...@me.com> wrote: >> >> I would sooner get the right answer slowly than the wrong answer quickly. >> >> Regards, Rob. >> >>> On 7 Sep 2017, at 13:48, Raul Miller <rauldmil...@gmail.com> wrote: >>> >>> Those proposals would cause operations on large arrays to >>> intermittently stall or spam. >>> >>> FYI, >>> >>> -- >>> Raul >>> >>> >>>> On Thu, Sep 7, 2017 at 7:54 AM, Rob B <rb75...@me.com> wrote: >>>> Thanks Raul, I am familiar with these ideas, and using x: is almost a >> reflex now. >>>> >>>> I feel that to protect the new J user, mod should convert to extended >> precision automatically or issue an warning message. Giving tha answer zero >> is very misleading. >>>> >>>> PS I am not so concerned with small numbers and measurability as with >> large numbers and primality. Heisenberg's Uncertainty Principle is not >> usually an issue for me :) >>>> >>>> Ragards, Rob. >>>> >>>>> On 7 Sep 2017, at 11:32, Raul Miller <rauldmil...@gmail.com> wrote: >>>>> >>>>> The answer, oddly enough, is: yes. >>>>> >>>>> The philosophical arguments are buried here: >>>>> >>>>> https://en.wikipedia.org/wiki/Accuracy_and_precision >>>>> >>>>> The technical issues are buried here: >>>>> >>>>> https://en.wikipedia.org/wiki/IEEE_754 >>>>> >>>>> That said, if you have reason to be using numbers which are precise >>>>> beyond anyone's ability to measure (and keep in mind Heisenberg >>>>> Uncertainty as one of the practical limits on measurability), you >>>>> should probably be using extended precision numbers (123x instead of >>>>> 123). This will give you exact results in exchange for a performance >>>>> penalty. >>>>> >>>>> Thanks, >>>>> >>>>> -- >>>>> Raul >>>>> >>>>> >>>>>> On Thu, Sep 7, 2017 at 4:42 AM, Rob B <rb75...@me.com> wrote: >>>>>> On reflection my real question is; should mod suddenly and without >> warning give the wrong answer when a number gets suffiently large? I have >> been caught by this many times. The incorrect answer zero is problematic as >> it suggests divisibility. >>>>>> >>>>>> Apologies if this has all been discussed before. >>>>>> >>>>>> Regards, Rob Burns. >>>>>> >>>>>> >>>>>> >>>>>>> On 6 Sep 2017, at 09:11, Rob B <rb75...@icloud.com> wrote: >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> I now see it's reasonable for ^ to convert to flost and *: to remain >> exact. >>>>>>> >>>>>>> The other discrepancy is probably due to my old version, iPad 701. >>>>>>> >>>>>>> Regards, Rob Burns. >>>>>>> >>>>>>>> On 5 Sep 2017, at 17:48, HenryRich <henryhr...@gmail.com> wrote: >>>>>>>> >>>>>>>> datatype 47^2 >>>>>>>> >>>>>>>> floating >>>>>>>> >>>>>>>> >>>>>>>> So >>>>>>>> >>>>>>>> (n^2) | 5729082486784839 >>>>>>>> >>>>>>>> is promoted to float, and loses precision. Same when the big >> number is extended - it's converted to float. >>>>>>>> >>>>>>>> For >>>>>>>> >>>>>>>> (x: n^2) | 5729082486784839 >>>>>>>> >>>>>>>> I get 147 as the result. >>>>>>>> >>>>>>>> Henry Rich >>>>>>>> >>>>>>>>> On 9/5/2017 12:41 PM, Rob B wrote: >>>>>>>>> Could someone explain this please? >>>>>>>>> >>>>>>>>> n=.14 >>>>>>>>> n >>>>>>>>> 14 >>>>>>>>> (*: n) | 5729082486784839 >>>>>>>>> 147 >>>>>>>>> 196 | 5729082486784839 >>>>>>>>> 147 >>>>>>>>> (n^2) | 5729082486784839 >>>>>>>>> 0 >>>>>>>>> (n^2) | 5729082486784839x >>>>>>>>> 0 >>>>>>>>> (x: n^2) | 5729082486784839 >>>>>>>>> 0 >>>>>>>>> (x: n^2) | 5729082486784839x >>>>>>>>> 147 >>>>>>>>> >>>>>>>>> >>>>>>>>> Regards, Rob Burns >>>>>>>>> ------------------------------------------------------------ >> ---------- >>>>>>>>> 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
