#11239: Incorrect coercion of polynomials over finite fields
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Reporter: johanbosman | Owner: robertwb
Type: defect | Status:
Priority: major | needs_work
Component: coercion | Milestone:
Keywords: finite fields, polynomials, | sage-5.11
coercion | Resolution:
Authors: pbruin | Merged in:
Report Upstream: N/A | Reviewers:
Branch: | Work issues:
Stopgaps: | Dependencies: #8335
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Comment (by pbruin):
Replying to [comment:3 dkrenn]:
> It seems that everything that can be represented as polynomial is
converted in that way. The phenomenon also appears with quotient rings:
>
> {{{
> sage: R.<x> = ZZ[]
> sage: A.<a> = R.quotient(x^3+2); PA.<s> = A[]
> sage: B.<b> = R.quotient(x^5+3); PB.<t> = B[]
> sage: f = a*s^3 + a^2*s; f
> a*s^3 + a^2*s
> sage: PB(f)
> b*t^3 + b^2*t
> }}}
Debatable as it may seem, this is the behaviour currently described in the
documentation of `PolynomialQuotientRing_generic._element_constructor_()`.
Attempting a coercion (`PB.coerce(f)`) instead of a conversion (`PB(f)`)
does lead to
{{{
TypeError: no canonical coercion from Univariate Polynomial Ring in s over
Univariate Quotient Polynomial Ring in a over Integer Ring with modulus
x^3 + 2 to Univariate Polynomial Ring in t over Univariate Quotient
Polynomial Ring in b over Integer Ring with modulus x^5 + 3
}}}
as expected.
--
Ticket URL: <http://trac.sagemath.org/ticket/11239#comment:10>
Sage <http://www.sagemath.org>
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