#16203: conversion from SR.series() to PowerSeries(SR) gives unexpected result
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: algebra | Resolution:
Keywords: series conversion | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by rws:
Old description:
> {{{
> sage: R.<x> = PowerSeriesRing(SR)
> sage: var('y')
> y
> sage: ex=1/(1-y)
> sage: ex.series(y,20)
> 1 + 1*y + 1*y^2 + 1*y^3 + 1*y^4 + 1*y^5 + 1*y^6 + 1*y^7 + 1*y^8 + 1*y^9 +
> 1*y^10 + 1*y^11 + 1*y^12 + 1*y^13 + 1*y^14 + 1*y^15 + 1*y^16 + 1*y^17 +
> 1*y^18 + 1*y^19 + Order(y^20)
> sage: s=R(_); s
> 1 + y + y^2 + y^3 + y^4 + y^5 + y^6 + y^7 + y^8 + y^9 + y^10 + y^11 +
> y^12 + y^13 + y^14 + y^15 + y^16 + y^17 + y^18 + y^19 + Order(y^20)
> sage: type(s)
> <type 'sage.rings.power_series_poly.PowerSeries_poly'>
> sage: s.list()
> [1 + 1*y + 1*y^2 + 1*y^3 + 1*y^4 + 1*y^5 + 1*y^6 + 1*y^7 + 1*y^8 + 1*y^9
> + 1*y^10 + 1*y^11 + 1*y^12 + 1*y^13 + 1*y^14 + 1*y^15 + 1*y^16 + 1*y^17 +
> 1*y^18 + 1*y^19 + Order(y^20)]
> }}}
> The correct result would be `1 + x + x^2...`. Obviously `Order(20)` is
> not recognized as a marker for the existence of a power series. The whole
> symbolic expression is taken as a constant.
>
> Also reported in http://ask.sagemath.org/question/24777/how-to-convert-a
> -taylor-polynomial-to-a-power-series/
New description:
{{{
sage: R.<x> = PowerSeriesRing(SR)
sage: var('y')
y
sage: ex=1/(1-y)
sage: ex.series(y,20)
1 + 1*y + 1*y^2 + 1*y^3 + 1*y^4 + 1*y^5 + 1*y^6 + 1*y^7 + 1*y^8 + 1*y^9 +
1*y^10 + 1*y^11 + 1*y^12 + 1*y^13 + 1*y^14 + 1*y^15 + 1*y^16 + 1*y^17 +
1*y^18 + 1*y^19 + Order(y^20)
sage: s=R(_); s
1 + y + y^2 + y^3 + y^4 + y^5 + y^6 + y^7 + y^8 + y^9 + y^10 + y^11 + y^12
+ y^13 + y^14 + y^15 + y^16 + y^17 + y^18 + y^19 + Order(y^20)
sage: type(s)
<type 'sage.rings.power_series_poly.PowerSeries_poly'>
sage: s.list()
[1 + 1*y + 1*y^2 + 1*y^3 + 1*y^4 + 1*y^5 + 1*y^6 + 1*y^7 + 1*y^8 + 1*y^9 +
1*y^10 + 1*y^11 + 1*y^12 + 1*y^13 + 1*y^14 + 1*y^15 + 1*y^16 + 1*y^17 +
1*y^18 + 1*y^19 + Order(y^20)]
}}}
The correct result would be `1 + x + x^2...`. Obviously `Order(20)` is not
recognized as a marker for the existence of a power series. The whole
symbolic expression is taken as a constant.
Also reported in http://ask.sagemath.org/question/24777/how-to-convert-a
-taylor-polynomial-to-a-power-series/ and
http://ask.sagemath.org/question/24968/coefficients-in-polynomial-ring-
over-symbolic-ring/
--
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Ticket URL: <http://trac.sagemath.org/ticket/16203#comment:4>
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