> sage seems to think that the gcd of 6 and (-2 mod 6) is -2 mod 6, which it > converts to 4. A mathematician would say that the gcd is 2. > Is this a bug, or does sage have a higher purpose here?
Sage is actually reasoning slightly differently, I think. First it decides whether there's a canonical coercion to a common parent. In this case, it concludes that the common parent should be the ring of integers modulo 6: sage: parent(Mod(4,6)) Ring of integers modulo 6 sage: parent(6) Integer Ring sage: z = cm.canonical_coercion(Mod(4,6), 6) sage: z (4, 0) sage: parent(z[0]), parent(z[1]) (Ring of integers modulo 6, Ring of integers modulo 6) There's no gcd method defined in this ring, so it falls back to attempting to coerce 4 mod 6 and 0 mod 6 to ZZ, which succeeds, and we get the integer version under which we have sage: gcd(4,0) 4 It's not clear to me what the best way to handle this case is. Paging Simon King.. :^) Doug -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
