On Jul 5, 2008, at 7:16 PM, John H Palmieri wrote: >> >>> would be good enough? (That is, assuming I've defined a reasonable >>> __eq__ method for the parents, the SteenrodAlgebra class.) >> >> Yes, though that will mean something like A5.P(2) - A5.P(2) == 0 will >> return False. This is why you are better off using _cmp_ instead of >> __eq__, __ne__, __le__, __gt__, ... (also, the latter are deprecated >> in Python). The _cmp_ method will always be called with two things of >> the same parent, invoking coercion if necessary. >> > > I think I understand this, but I have one more problem. I think you're > saying that I'm supposed to get rid of __eq__ and define __cmp__ > instead, with no error checking -- assume that the two arguments have > the same parent. I have done this, and __cmp__ just checks whether > the difference x-y is the zero element of the algebra. > > Now I get the following, which is good: > > sage: A5.P(2) == A7.P(2) > False > sage: A5.P(2) - A5.P(2) == 0 > True > sage: 2 * A5.P(2) > 2 P(2) > sage: 10 * A7.P(2) # working mod 7 > 3 P(2) > > On the other hand, > > sage: cmp(A5.P(2), A7.P(2)) > > gives an error message: "unsupported operand parent(s) for '-': 'mod 5 > Steenrod algebra' and 'mod 7 Steenrod algebra' " > > (Same thing happens with 'A5.P(2).__cmp__(A7.P(2))', but cmp(A5(3), > 3) returns 0, as it should.) > > Why doesn't cmp() work, or is this what's supposed to happen? (I can > add type-checking to the definition of __cmp__, in which case the > above command returns -1, but it sounded like you were saying that I > shouldn't have to.) > > Thanks for taking the time to answer all of my silly questions, by the > way. I think this might be the last one for now.
What does A5 == A7 give you? Can you do A5.P(2) == A7.P(2)? I'm not sure exactly what's going on here, but as long as the above is working well enough for now it's probably worth holding off debugging too much until the new coercion is in place (which is more likely than not to resolve this). - 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 -~----------~----~----~----~------~----~------~--~---
