#10950: The hash function for matrices suffers from many collisions with
permutation matrices
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Reporter: nthiery | Owner: nthiery
Type: defect | Status: new
Priority: major | Milestone:
Component: linear algebra | Resolution:
Keywords: Weyl groups, permutation | Merged in:
matrices, hash |
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by nbruin):
This is still true. I'd say it's just true of "dense" collections of
matrices:
{{{
def imm(A):
A.set_immutable()
return A
}}}
{{{
sage: V={imm(matrix([a,b,c,d])) for a in [-1..1] for b in [-1..1] for c in
[-1..1] for d in [-1..1]}
sage: H={hash(v) for v in V}
sage: Ht={hash(tuple(v.list())) for v in V}
sage: len(V); len (H); len(Ht)
81
14
69
}}}
so I think this problem might need a little bump in priority.
--
Ticket URL: <https://trac.sagemath.org/ticket/10950#comment:6>
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