On Jul 4, 10:53 am, Robert Bradshaw <[EMAIL PROTECTED]>
wrote:
> On Jul 4, 2008, at 10:44 AM, John H Palmieri wrote:
>
>
>
>
>
> >>> 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.
>
> > Here's an example.
>
> > sage: A5 = SteenrodAlgebra(5); A7 = SteenrodAlgebra(7)
> > sage: A5 == A7
> > False
> > sage: v = A5.P(2)
> > sage: w = A7.P(2,1)
> > sage: 2 * v
> > 2 P(2)
> > sage: 3 * w
> > ----------------------------------------------------------------------
> > -----
> > TypeError Traceback (most recent call
> > last)
>
> > /Users/palmieri/<ipython console> in <module>()
>
> > /Users/palmieri/element.pyx in
> > sage.structure.element.RingElement.__mul__ (sage/structure/element.c:
> > 8545)()
>
> > /Users/palmieri/coerce.pyx in
> > sage.structure.coerce.CoercionModel_cache_maps.bin_op_c (sage/
> > structure/coerce.c:5039)()
>
> > /Users/palmieri/coerce.pyx in
> > sage.structure.coerce.CoercionModel_cache_maps.get_action_c (sage/
> > structure/coerce.c:7864)()
>
> > /Users/palmieri/coerce.pyx in
> > sage.structure.coerce.CoercionModel_cache_maps.discover_action_c
> > (sage/
> > structure/coerce.c:8522)()
>
> > /Users/palmieri/parent.pyx in
> > sage.structure.parent.Parent.get_action_c (sage/structure/parent.c:
> > 1843)()
>
> > /Users/palmieri/parent.pyx in
> > sage.structure.parent.Parent.get_action_impl (sage/structure/parent.c:
> > 2005)()
>
> > /Users/palmieri/parent.pyx in
> > sage.structure.parent.Parent.get_action_c_impl (sage/structure/
> > parent.c:2672)()
>
> > /Users/palmieri/parent.pyx in sage.structure.parent._register_pair
> > (sage/structure/parent.c:6360)()
>
> > /Users/palmieri/parent.pyx in sage.structure.parent.EltPair.__eq__
> > (sage/structure/parent.c:6183)()
>
> > /Applications/sage/local/lib/python2.5/site-packages/sage/algebras/
> > steenrod_algebra.py in __eq__(self, other)
> > 1528 Two elements are equal if their difference is zero.
> > 1529 """
> > -> 1530 difference = self - other
> > 1531 return len(difference._raw['milnor']) == 0
> > 1532
>
> > /Users/palmieri/element.pyx in
> > sage.structure.element.ModuleElement.__sub__ (sage/structure/
> > element.c:
> > 5421)()
>
> > /Users/palmieri/coerce.pyx in
> > sage.structure.coerce.CoercionModel_cache_maps.bin_op_c (sage/
> > structure/coerce.c:5338)()
>
> > TypeError: unsupported operand parent(s) for '-': 'mod 7 Steenrod
> > algebra' and 'mod 5 Steenrod algebra'
>
> Ah, it looks like your __eq__ method is assuming that self and other
> are elements of the steenrod algebra. There are two solutions to this:
>
> 1) Use __cmp__ which (in Sage) will ensure that self and other have
> the same parent before it's called
> 2) Fix your __eq__ (and any other comparison methods you might have)
> to make sure self-other makes sense (or, as a quick fix, catch the
> type error here).
>
I still don't understand two things: why the gen method is being used,
and why if I multiply an element of SteenrodAlgebra(7) by 3, somehow
elements of SteenrodAlgebra(5) are getting involved.
> - Robert
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