#15605: (-1)^(2/3) evaluates to 1
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Reporter: mmezzarobba | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by tmonteil):
Replying to [ticket:15605 mmezzarobba]:
> Likely a duplicate, but I couldn't find it elsewhere...
It is indeed a known issue since at least
[http://ask.sagemath.org/question/10063/get-variants-of-complex-cube-
root/?answer=14842#post-id-14842 this ask answer], and i use this example
in my presentations about Sage and the need to define objects within a
reliable parent.
I did not report that on trac because this is somehow a feature of the
symbolic ring : no semantics. I remember a discussion with you at sd49
(Orsay) about that precise example and the benefits (or not!) of having
such kind of symbolic expressions that are able to make all kind of
simplifications/derivatives/evaluations without context.
If one want to have something that both:
- applies rules such as `a^(bc) = (a^b)^c` systematically,
- takes principal branches of multi-valued complex function when
evaluating,
then we should accept that kind of behaviour.
It would however be awesome to have a well-designed object to work with
holomorphic functions, along the same lines that what is done with
polynomials, i guess it is a very hard task, and i do not know whether
there exists libraries for that.
--
Ticket URL: <http://trac.sagemath.org/ticket/15605#comment:7>
Sage <http://www.sagemath.org>
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