#4376: Implement conversion of power series over more rings (e.g. GF(p)) to pari
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Reporter: cremona | Owner: was
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-4.6.2
Component: interfaces | Keywords: power series pari
gp
Author: Francis Clarke, Jeroen Demeyer | Upstream: N/A
Reviewer: Marco Streng | Merged:
Work_issues: |
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Comment(by fwclarke):
Replying to [comment:9 jdemeyer]:
> Test failures on sage-4.6.2.alpha1:
> ...
What's happened is that #7644 means that many more series can be converted
to Pari and reversion performed using `sereverse`. But when the degree-
one coefficient is not a unit, converting the result back to Sage has
exposed the following problem:
{{{
sage: P.<x> = Q[]
sage: Q = P.fraction_field()
sage: Q(1/x)
1/x
sage: Q(pari(1/x))
0
}}}
This is caused by
{{{
sage: P(pari(1/x))
0
}}}
whereas `P(1/x)` raises `TypeError: denominator must be a unit`.
The other group of failures is caused when conversion to a Pari series is
successful but reversion raises a Pari error.
I will shortly post a patch which sorts these difficulties out. I've added
a doctest for `reversion` in order to provide another example where Pari
fails and the Lagrange inversion code needs to be used.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4376#comment:11>
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