#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 jpflori):
Replying to [comment:23 pbruin]:
> Replying to [comment:21 jpflori]:
> > Maybe this is worth a broader discussion on sage-devel...
> I think it is worth thinking about whether the "stupid" conversion
should be allowed between different quotients of a polynomial ring.
However, for the problem addressed in this ticket, there is really only
one sensible thing to do, namely applying the canonical map between the
base rings.
>
I agree.
> > Especially, should we let the stupid conversion in when there is no
coercion (as it seems to fit Sage's philosophy and it is in place for
quotients)?
> I personally think that allowing `Fqq['y'](f)` to 'desperately' apply
any available conversion, however nonsensical it may be, to the
coefficients is a bad idea. I don't see what is gained by permitting this
notation; it seems to make it far too easy for the user to unwittingy
introduce mysterious errors in this way. If someone really wants this
behaviour, it is much better to require explicitly lifting the finite
field elements to '''Z'''[''x''] or another suitable ring.
I completely agree, whence my previous positive review.
But the doc for coercion kind of make me think, humm, maybe some people
want the stupid behavior as well...
>
> I would be in favour of a less permissive approach for conversions
between different polynomial ring quotients as well, but again, this
ticket is not the place to decide that.
I agree as well, I was just menitoning it because it's already mentioned
here :)
Anyway, if nobody gives a strong opinion of why to keep conversions
without any mathematical sense and confusing for naive users on sage-
devel, then I'll put this back to positive review quickly as I think that
the situation with this ticket is far better.
Note that maybe some efficiency could be gained by replacing the
has_coerce_map_from by something else but I have no idea what to do now
and no time to think about it, I'd just like to remove the stupid
conversion unless someone convinces me to keep them of course.
--
Ticket URL: <http://trac.sagemath.org/ticket/11239#comment:24>
Sage <http://www.sagemath.org>
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