#20086: ZZ[X], QQ[X]: allow arbitrary powers of constant polynomials
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Reporter: cheuberg | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-7.1
Component: basic arithmetic | Resolution:
Keywords: | Merged in:
Authors: Clemens Heuberger | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/cheuberg/polynomials/power | 918499cf377a551a5e28ea1d6748ed50860f1afa
Dependencies: | Stopgaps:
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Comment (by cheuberg):
Replying to [comment:6 nbruin]:
> The fact that for a in QQ, the value of `a^(1/2)` has its parent
depending on the actual value of a is a compromise for novice use (in
calculus etc.) Normally, one would raise an error if `a^(1/2)` does not
lie in QQ. Certainly, promoting to SR is a very bad choice for anything
else than novice use.
>
> I see you take the effort of trying to put the result back in the
original parent. Don't you think it's better to force that? i.e., raise an
error if it doesn't work, rather than give a result back in SR?
>
> The problem is that if someone is computing with polynomials, it's
almost certainly not desired to end up in SR (where things like
`QQ['x']['x']` get squashed), and if an error isn't raised, it's very hard
to detect that it happened.
very valid points, thank you. I now raise an exception.
>
> Also, if you're implementing the (partial) map `a:->a^(n/m)` , why not
extend it properly? When
> `(QQ['x'](4))^(1/2)` works, why should `QQ['x'](x^2)^(1/2)` fail?
I needed a fix a bug which did bite me somewhere else, see initial
description. Of course, it would be nice to have that, too; but I'd prefer
to leave that to a follow-up ticket and to have this functionality here
soon.
--
Ticket URL: <http://trac.sagemath.org/ticket/20086#comment:9>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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