#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):
Replying to [comment:14 SimonKing]:
> I will have a closer look at sqrt - perhaps I'll find something.
It seems so.
First, the reason why the old version failed for a power series over ZZ is
the fact that the invert method raises an error if the result has
coefficients in QQ rather than ZZ. I guess this must change.
Second, there is a division inside the sqrt method. By my patch, this
division returns a Laurent series, which slows things slightly down. If I
do ``a*s.__invert__()`` instead of ``a/s`` then the timings are as good as
with the old code.
So, there will soon be a third patch...
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8972#comment:15>
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