On Jul 5, 10:08 am, Robert Bradshaw <[EMAIL PROTECTED]>
wrote:
> On Jul 4, 2008, at 1:52 PM, John H Palmieri wrote:
>
>
>
>
>
> > 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.
>
> I'm not seeing where the gen method is being used--it's probably to
> get a "generic" element to see if multiplication is a viable option.
> As for elements of SteenrodAlgebra(7) and SteenrodAlgebra(5) getting
> compared, that's because it's looking up something in a (global-ish)
> lookup table that happens to have SteenrodAlgebra(5) in it as well.
> Obviously equality here should return False.
>
So, for example, for the definition of the __eq__ method for
SteenrodAlgebraElement, replacing
difference = self - other
return len(difference._raw['milnor']) == 0
with
if self.parent() == other.parent():
difference = self - other
return len(difference._raw['milnor']) == 0
else:
return False
would be good enough? (That is, assuming I've defined a reasonable
__eq__ method for the parents, the SteenrodAlgebra class.)
> - Robert
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