#20490: Hash error with multivariate Laurent polynomial rings
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Reporter: tscrim | Owner: tscrim
Type: defect | Status: new
Priority: critical | Milestone: sage-7.2
Component: misc | Resolution:
Keywords: hash, multivariate Laurent | Merged in:
polynomials | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: |
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Comment (by roed):
The problem is that the hash function takes `elt._mon` into account:
internally `elt` is represented as `ab/ab` while `R.one()` is represented
as `1/1`.
{{{
sage: elt._fraction_pair()
(a*b, a*b)
sage: R.one()._fraction_pair()
(1, 1)
}}}
The problem is solved in this case by manually calling `_normalize()`:
{{{
sage: elt._normalize()
sage: elt._fraction_pair()
(1, 1)
sage: hash(elt) == hash(R.one())
True
}}}
Writing hash functions is hard....
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Ticket URL: <http://trac.sagemath.org/ticket/20490#comment:1>
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