On Jul 4, 2008, at 7:12 AM, John H Palmieri wrote: > I'm running into a coercion problem. I'm trying to define a class > SteenrodAlgebra (based on the Algebra class); there should be one > Steenrod algebra for each prime number p, and it is an algebra over > GF(p). For example, you can do > > sage: A5 = SteenrodAlgebra(5) > sage: A7 = SteenrodAlgebra(7)
I just tried these lines, where do I import SteenrodAlgebra from? (Or is it not in standard Sage yet?) > I have coercion working properly for addition, but not multiplication, > and I really don't know why. One way to define elements is to use a > method called "P": > > sage: v = A5.P(1,2,3) > sage: w = A7.P(4,5) > > The identity element of the Steenrod algebra is called P(0), and I > have a _coerce_impl method which seems to work: it seems to coerce a > scalar into the appropriate scalar multiple of P(0): > > sage: 3 + v > 3 P(0) + P(1,2,3) > sage: 11 + w # addition here is mod 7 > 4 P(0) + P(4,5) > > Multiplication is broken, though: > > sage: 3 * v # this works > 3 P(1,2,3) > sage: 11 * w > > gives me a traceback, and it appears that the problem is that Sage is > testing whether A5.gen(0) is equal to A7.gen(0). Why is A7.gen(0) > involved? I mean, w is in A7, but why is Sage interested in its 0th > generator? And why is A5.gen(0) involved in this at all, when I'm > trying to multiply an element of A7 by an integer (which should coerce > to an element of GF(7), and then into A7)? If I interchange the order > of evaluation here, doing 11 * w before 3 * v, then 11 * w works, > while 3 * v gives the error. By putting in some print statements in > various places, I can see that even when 3 * v works, it is still > calling A5.gen(0) the first time it is called; subsequent times, it > doesn't call this. (Is Sage caching information about generators > somewhere, and is that perhaps causing problems, because I've done > something wrong and not distinguished sufficiently between Steenrod > algebras at different primes?) > > So I'm very confused. Any ideas what I should look at to try to fix > this? Yes, Sage caches some information so it doesn't have to do the logic anew on each arithmetic operation. One thing to check is if A5 == A7 succeeds. If you could post the traceback I could see if anything stands out to me. - Robert --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
