#19016: Better hash for Element
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Reporter: | Owner:
ncohen | Status: needs_work
Type: | Milestone: sage-6.9
defect | Resolution:
Priority: | Merged in:
blocker | Reviewers:
Component: misc | Work issues:
Keywords: | Commit:
Authors: | 754dc5794a1a7004c8844cf7cfb64220957c36a5
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
u/ncohen/19016 |
Dependencies: |
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Comment (by vdelecroix):
Replying to [comment:37 nbruin]:
> Replying to [comment:35 vdelecroix]:
> > In other words, any (additive or multiplicative) magma element should
be immutable or adopt an mutable/immutable framework... might be a lot of
work to fix!
>
> No, worse: any magma should have a decidable equality notion and a hash
that's compatible with it.
Nope. To fix just these `test_zero` and `test_one` one way is to allow to
hash the unit but no other elements... does it look reasonable from the
point of view of this ticket? Whether we want to do better looks for me as
a part #19038.
New bad news: hashing of ideals. The `ResidueField` factory in
`sage.rings.finite_rings.residue_field` uses as keys ideals that do not
implement hashing. And I guess in most non trivial case having a hash
value would be hard. For principal ideal, it is easy to test equality but
much harder to implement a hash.
--
Ticket URL: <http://trac.sagemath.org/ticket/19016#comment:38>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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