#8972: Inversion and fraction fields for power series rings
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Reporter: SimonKing | Owner: AlexGhitza
Type: defect | Status: needs_work
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: improve timings |
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Comment(by SimonKing):
Replying to [comment:8 SimonKing]:
> Concerning timings, I see a couple of things that might help improve the
div method:
One more thing: The old code is quick if the result actually belongs to
the power series ring, which is quite often the case; if this is not the
case then often an error results. And I guess the parent should always be
the fraction field, eventually.
What I just tested (but I really should get some sleep now...) is to cache
the fraction_field method, and to ''try'' to use the old code if the
valuation of the denominator is not bigger than the valuation of the
numerator; if this fails, then put numerator and denominator into the
fraction field, and try again.
Doing so brings the above timing to about 2ms, which is still a loss of
factor two, but two is less than 5 or 6. I'll submit another patch after
trying to lift the dependency of the two div methods on each other.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8972#comment:9>
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