#13856: Add a top_class method to the Steenrod algebra
--------------------------------------+-------------------------------------
Reporter: cnassau | Owner: jhpalmieri
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.7
Component: algebraic topology | Resolution:
Keywords: Steenrod algebra | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Christian Nassau | Merged in:
Dependencies: | Stopgaps:
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Comment (by jhpalmieri):
Perhaps for another ticket: I think your code reveals a bug. What do you
think about this change:
{{{
#!diff
diff --git a/sage/algebras/steenrod/steenrod_algebra.py
b/sage/algebras/steenrod/steenrod_algebra.py
--- a/sage/algebras/steenrod/steenrod_algebra.py
+++ b/sage/algebras/steenrod/steenrod_algebra.py
@@ -2008,8 +2008,9 @@
else:
a = x.milnor()
if self.basis_name() == 'milnor':
- return a
- return a.change_basis(self.basis_name())
+ return self._from_dict(a.monomial_coefficients(),
coerce=True)
+ a = a.change_basis(self.basis_name())
+ return self._from_dict(a.monomial_coefficients(),
coerce=True)
raise ValueError("Element does not lie in this Steenrod algebra")
def __contains__(self, x):
}}}
As it stands:
{{{
sage: SteenrodAlgebra(2,profile=(3,2,1), basis='pst')(Sq(4)).parent()
mod 2 Steenrod algebra, pst_revz basis
}}}
With the change:
{{{
sage: SteenrodAlgebra(2,profile=(3,2,1), basis='pst')(Sq(4)).parent()
sub-Hopf algebra of mod 2 Steenrod algebra, pst_revz basis, profile
function [3, 2, 1]
}}}
My suggested patch would need some doctests, but it would also allow you
to change your last line:
{{{
#!diff
diff --git a/sage/algebras/steenrod/steenrod_algebra.py
b/sage/algebras/steenrod/steenrod_algebra.py
--- a/sage/algebras/steenrod/steenrod_algebra.py
+++ b/sage/algebras/steenrod/steenrod_algebra.py
@@ -2821,7 +2822,7 @@
e = [k for k in range(0,len(ep)) if ep[k]==2]
r = [p**k-1 for k in rp]
ans = AM.monomial((tuple(e),tuple(r)))
- return self(ans.change_basis(self.basis_name()))
+ return self(ans)
def order(self):
r"""
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13856#comment:4>
Sage <http://www.sagemath.org>
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