On Jul 17, 3:30 pm, John H Palmieri <[EMAIL PROTECTED]> wrote: > I have several different vector space bases for an algebra A, and I > have implemented this by having a class MyAlgebra, instances of which > have an attribute _basis_name which is a string naming the basis. I > have __cmp__ defined so that the basis is ignored: any two instances > are canonically isomorphic, and there is good coercion between them. > > Now, the attribute _basis_name just affects the _repr_ and _latex_ > methods for elements of the algebra; it has no other effect. My > question is this: when I multiply elements from algebras with two > different bases, I can't figure out how the parent of the result is > determined. Some documentation suggests that the parent should be > determined by the left factor, but that is not consistently what's > happening. > > I think I would like to force the result to have the same parent as > the left-hand factor, but by the time elements get to the _mul_ > method, their parents have been changed (via coercion), so I can't > find out what that parent is. (Perhaps something is getting cached in > the coercion process, so things are getting coerced to the cached > algebra, not the left-hand parent?) What should I do? Does it sound > like I'm doing something wrong, and if so, what should I investigate?
Currently it's built-in to coercion that if two parents are equal, then it doesn't matter which parent it picks. (And the decision is baked into various caches, etc., so the decision can depend on the previous history of commands in this session.) I've raised this issue as a problem a few weeks ago (see http://groups.google.com/group/sage-devel/browse_thread/thread/4520ed454e705ce1#), but nothing came of it yet. Even if this gets fixed, I don't think you can fix it so that coercion uses the parent of the left-hand value by changing your code; this would require changes inside the base coercion code. Carl --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@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-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
