#18462: hash of finitely presented group element
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Reporter: kalvotom | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.8
Component: group theory | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by kalvotom:
Old description:
> It looks like the cayley_graph of finitely presented group is broken in
> Sage 6.7.
>
> For example, cayley_graph of Klein group returns a graph with 14
> vertices:
>
> {{{
> sage: groups.presentation.KleinFour().cayley_graph()
> Digraph on 14 vertices
> }}}
>
> On the other hand in Sage 6.6 one gets the correct graph with 4 vertices:
>
> {{{
> sage: groups.presentation.KleinFour().cayley_graph()
> Launched png viewer for Digraph on 4 vertices
> }}}
New description:
Two equal elements of a finitely presented group does not have equal hash.
For example:
{{{
sage: G=groups.presentation.KleinFour()
sage: a,b=G.generators()
sage: a^3 == a
True
sage: hash(a^3)
1453079729248098375
sage: hash(a)
12416037344
}}}
Consequently, cayley_graph of finitely presented group is broken:
{{{
sage: groups.presentation.KleinFour().cayley_graph()
Digraph on 14 vertices
}}}
One would expect a graph with 4 vertices only.
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Ticket URL: <http://trac.sagemath.org/ticket/18462#comment:6>
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