#3979: Power series composition messes up precision
--------------------------------------------------------+-------------------
Reporter: kedlaya | Owner:
somebody
Type: defect | Status:
positive_review
Priority: critical | Milestone:
sage-5.4
Component: algebra | Resolution:
Keywords: power series, composition, precision | Work issues:
Report Upstream: N/A | Reviewers: Kiran
Kedlaya, Luis Felipe Tabera Alonso, Frédéric Chapoton
Authors: Francis Clarke | Merged in:
Dependencies: | Stopgaps: 12783
--------------------------------------------------------+-------------------
Description changed by fwclarke:
Old description:
> The composition of two power series is sometimes returned with the wrong
> precision. A trivial example:
>
> {{{
> sage: pow.<u> = PowerSeriesRing(Rationals()); print (1 + O(u^4))(u)
> 1
> }}}
> where the return value should have precision 4 rather than infinity. A
> more nontrivial example:
>
> {{{
> sage: pow.<u> = PowerSeriesRing(Rationals()); print (1 + u^2 +
> O(u^4))(u^2)
> 1 + u^4 + O(u^10)
> }}}
> where the return value should have precision 8 instead of 10.
>
> ----
>
> Apply
> * [attachment:trac_3979_power_series_substitution_rev4.patch]
> * [attachment:trac_3979_power_series_substitution_rev4_extra.patch]
New description:
The composition of two power series is sometimes returned with the wrong
precision. A trivial example:
{{{
sage: pow.<u> = PowerSeriesRing(Rationals()); print (1 + O(u^4))(u)
1
}}}
where the return value should have precision 4 rather than infinity. A
more nontrivial example:
{{{
sage: pow.<u> = PowerSeriesRing(Rationals()); print (1 + u^2 +
O(u^4))(u^2)
1 + u^4 + O(u^10)
}}}
where the return value should have precision 8 instead of 10.
----
Apply
* [attachment:trac_3979_power_series_substitution_rev4.patch]
* [attachment:trac_3979_power_series_substitution_rev4_extra.patch]
*
[attachment:trac_3979_power_series_substitution_rev4_supplementary.patch]
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/3979#comment:27>
Sage <http://www.sagemath.org>
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