#11239: Incorrect coercion of polynomials over finite fields
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Reporter: johanbosman | Owner: robertwb
Type: defect | Status: needs_info
Priority: major | Milestone: sage-6.1
Component: coercion | Resolution:
Keywords: finite fields, | Merged in:
polynomials, coercion, sd53 | Reviewers: Jean-Pierre Flori
Authors: Peter Bruin | Work issues:
Report Upstream: N/A | Commit:
Branch: | 236effb6198c6192dce0cedc0e53423c68743e3e
u/jpflori/ticket/11239 | Stopgaps:
Dependencies: #8335 |
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Comment (by SimonKing):
Replying to [comment:26 pbruin]:
> Replying to [comment:25 SimonKing]:
> > See my answer on sage-devel. In a nutshell: I would recommend against
doing expensive tests when talking about conversion, and I would be rather
permissive in conversions.
> >
> > Conversions have no defined properties, and thus there is nothing that
one could test.
>
> Given that a conversion needs to coincide with the coercion if the
latter exists, one must check for a coercion before applying the "stupid"
conversion (assuming the "stupid" conversion is desired at all).
No!! It is just the other way around! Ideally, you have a fast cheap
stupid conversion, and then a potentially expensive tests tells you
whether this conversion qualifies as a coercion. This, by the way, is
exactly what happens when `R._coerce_map_from_(S)` returns True: The
return value asserts that the conversion qualifies as a coercion.
> That is actually what I was trying to say on sage-devel in the context
of polynomial ring quotients, but I wasn't very clear. I agree that the
existence of coercion doesn't have to be transitive, or to satisfy any
rules;
You mean, conversion, not coercion? Coercion must be transitive. That's
one of the axioms.
--
Ticket URL: <http://trac.sagemath.org/ticket/11239#comment:27>
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