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
