On Fri, Feb 5, 2016 at 11:24 AM, Bruno Grenet <bruno.gre...@gmail.com> wrote: > Note that there is a difference between the example in the original email > and the answers: The original email was about is_prime(something) not > something.is_prime(). I do not know the mechanisms behind > is_prime(something) but would it be possible that in this case the behavior > is slightly different, say that the input is coerced to ZZ if possible? It > would be more user friendly I guess.
-1 to (2/1).is_prime() != is_prime(2/1). That just seems like a way to increase confusion even further. > Bruno > > > On 5 février 2016 19:59:53 HNEC, William Stein <wst...@gmail.com> wrote: >> >> >> >> On Friday, February 5, 2016, David Roe <roed.m...@gmail.com> wrote: >>> >>> >>> >>> On Fri, Feb 5, 2016 at 1:20 PM, Vincent Delecroix >>> <20100.delecr...@gmail.com> wrote: >>>> >>>> Hello, >>>> >>>> Indeed, the definition given in the documentation of "is_prime" does not >>>> coincide with what the method is doing. >>>> >>>> The mathematical definition of prime *depends* on the ring. An element >>>> of a ring is prime if the ideal it generates is prime. And the ideal (3) is >>>> prime in ZZ but not in QQ. A less stupid example >>>> >>>> sage: K = ZZ[I] >>>> sage: K(3).is_prime() >>>> True >>>> sage: K(5).is_prime() >>>> False >>>> >>>> The Sage behavior of the function is_prime is perfectly coherent with >>>> respect to this definition. >>>> >>>> I would rather make a patch to modify the documentation and warns the >>>> user about the difference between prime element in a ring and prime number. >>> >>> >>> +1 >>> David >> >> >> Maybe is_prime for field elements should just raise an exception? >> >> >>>> >>>> >>>> >>>> Vincent >>>> >>>> >>>> On 05/02/16 14:50, David Wong wrote: >>>>> >>>>> prime_number = bignumber / 2 >>>>> is_prime(prime_number) # -> False >>>>> >>>>> prime_number = bignumber // 2 >>>>> is_prime(prime_number) # -> True >>>>> >>>>> prime_number = ZZ(bignumber / 2) >>>>> is_prime(prime_number) # -> True >>>>> >>>>> >>>>> I've spent a couple of days arguing with people about a number (not) >>>>> being >>>>> a prime. Turns out it fails silently if you're in the wrong field. >>>>> >>>>> I guess a fix would be to ZZ() the number first in the function >>>>> is_prime. >>>>> If you guys agree I can submit a patch or something (never touched at >>>>> Sage's codebase and that would be a good opportunity) >>>>> >>>>> David >>>>> >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "sage-devel" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to sage-devel+unsubscr...@googlegroups.com. >>>> To post to this group, send email to sage-devel@googlegroups.com. >>>> Visit this group at https://groups.google.com/group/sage-devel. >>>> For more options, visit https://groups.google.com/d/optout. >>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sage-devel" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to sage-devel+unsubscr...@googlegroups.com. >>> To post to this group, send email to sage-devel@googlegroups.com. >>> Visit this group at https://groups.google.com/group/sage-devel. >>> For more options, visit https://groups.google.com/d/optout. >> >> > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To post to this group, send email to sage-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-devel. > For more options, visit https://groups.google.com/d/optout. -- William (http://wstein.org) -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
