#9457: power series comparison should use padded_list
-------------------------------------+-------------------------------------
Reporter: niles | Owner: malb
Type: defect | Status: needs_work
Priority: major | Milestone: sage-6.1
Component: commutative | Resolution:
algebra | Merged in:
Keywords: | Reviewers:
Authors: niles | Work issues: resolve problems with
Report Upstream: N/A | sha_tate.py
Branch: | Commit:
u/niles/ticket/9457 | e2219602a9d360f465ad79b098e4f923765ab791
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Old description:
> Comparison of power series uses list instead of padded_list; this means
> that power series equality can fail:
>
> {{{
> sage: A.<t> = PowerSeriesRing(ZZ)
> sage: g = t + t^3 + t^5 + O(t^6); g
> t + t^3 + t^5 + O(t^6)
> sage: [g == g.add_bigoh(i) for i in range(7)]
> [True, False, True, False, True, False, True]
> sage: g.add_bigoh(3).list()
> [0, 1]
> sage: g.add_bigoh(3).padded_list()
> [0, 1, 0]
> }}}
>
> == Apply ==
>
> * [attachment:trac_9457_power_series_eq_rebase.patch]
New description:
Comparison of power series uses `list` instead of `padded_list`. This
drops trailing zeros, and means that power series equality is buggy:
{{{
sage: A.<t> = PowerSeriesRing(ZZ)
sage: g = t + t^3 + t^5 + O(t^6); g
t + t^3 + t^5 + O(t^6)
sage: [g == g.add_bigoh(i) for i in range(7)] # these should all be
True
[True, False, True, False, True, False, True]
sage: g.add_bigoh(3).list() # drops trailing zero
[0, 1]
sage: g.add_bigoh(3).padded_list()
[0, 1, 0]
}}}
== Apply ==
* [attachment:trac_9457_power_series_eq_rebase.patch]
--
Comment (by niles):
I had hoped the changes at #12555 would magically resolve this, but they
do not. The other related tickets, listed in comment [comment:14] are
also not fixed by #12555.
Note that the current version of the git branch for this ticket (commit
e221960) does *not* include the changes of #12555, although the initial
version mistakenly did.
--
Ticket URL: <http://trac.sagemath.org/ticket/9457#comment:23>
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