#8972: Inversion and fraction fields for power series rings
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Reporter: SimonKing | Owner: AlexGhitza
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.4.2
Component: algebra | Keywords: power series ring, fraction field
Author: Simon King | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by SimonKing):
I forgot one remark:
I don't know how this happens, but the ``truncate`` method of Laurent
series behaves different than before, although the ``truncate`` method of
power series did not change:
{{{
sage: A.<t> = QQ[[]]
sage: f = (1+t)^100
sage: f.truncate(5)
3921225*t^4 + 161700*t^3 + 4950*t^2 + 100*t + 1
sage: f.truncate(5).parent()
Univariate Polynomial Ring in t over Rational Field
sage: g = 1/f
sage: g.truncate(5)
1 - 100*t + 5050*t^2 - 171700*t^3 + 4421275*t^4 + O(t^5)
sage: g.truncate(5).parent()
Laurent Series Ring in t over Rational Field
}}}
In other words, ``g.truncate(5)`` is now returning a Laurent series, but
without the patch it used to return return a univariate polynomial,
similar to ``f.truncate(5)``.
I don't know if this is acceptable, and also I don't understand how that
happened. Shall I change it?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8972#comment:11>
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