#7644: generic power series reversion
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Reporter: was | Owner: AlexGhitza
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-4.6.1
Component: algebra | Keywords: lagrange, reversion
Author: Niles Johnson | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by fwclarke):
I've been looking at this. One concern is that for power series with
rational coefficients the existing method using pari is a great deal
faster, so that at least in this case the pari method should be retained.
Strangely the existing method fails for integer power series, though pari
handles them perfectly ok.
On investigation it turns out that it is the conversion to pari which is
failing and that this problem is pointed out in
modular/overconvergent/genus0.py, and raised as #4376. I have produced a
short patch (awaiting review) which extends the range of base rings over
which pari conversion of a power series is possible.
What I propose then is that a revised patch (depending on the #4376 patch)
should try to use pari and that only if this fails should the Lagrange
inversion code be used.
I also think it is sensible to be able to revert infinite precision
series, either by specifying the desired precision or by using the
parent's default precision.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7644#comment:10>
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