On Fri, Feb 5, 2016 at 1:20 PM, Vincent Delecroix <[email protected] > 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 > > > 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 [email protected]. > To post to this group, send email to [email protected]. > 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
