#17427: x==y while hash(x)!=hash(y) with SchemeMorphism_point_projective_field
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Reporter: ncohen | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.5
Component: PLEASE CHANGE | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by bhutz):
Yes, I agree hashing over fields can just normalize the point before
hashing. For rings with 'nice' field of fractions, it could be coerced to
the FF, normalized, and then hashed. Over general rings (such as p-adics),
it sounds like you are proposing making projective points unhashable (as
is happening to p-adic numbers) instead of having a hash that doesn't
behave like a hash.
I'd have to experiment a little with that set-up to see if it causes any
additional issues. For example the points defined over the ring and the
fraction field with the same coordinates would then hash to the same
value. At the moment those points would be != since there is not yet a
coercion model for projective points and morphisms.
Overall, it seems like an ok proposal to me.
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Ticket URL: <http://trac.sagemath.org/ticket/17427#comment:7>
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