On Sun, Feb 19, 2012 at 8:25 PM, D. S. McNeil <dsm...@gmail.com> wrote: >> 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,
I think that we should define a gcd method for 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 -- William Stein Professor of Mathematics University of Washington http://wstein.org -- 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
