#10976: computing order of a certain subgroup of a permutation group is double
dog
slow (compared to Magma)
-----------------------------+----------------------------------------------
Reporter: was | Owner: swenson
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.0
Component: group theory | Keywords: sd32
Work_issues: | Upstream: N/A
Reviewer: William Stein | Author: Christopher Swenson
Merged: | Dependencies:
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Comment(by was):
Wow, at least one of those doctest failures shows that there is a mistake
in this algorithm:
{{{
sage: G = DihedralGroup(5).cayley_graph().automorphism_group()
sage: sage: G.order()
6
sage: G._gap_().Order()
10
sage: len(list(G))
10
}}}
I think that the author was perhaps assuming that the generators are all
transpositions, but didn't test this:
{{{
sage: G.gens()
[(1,8)(2,10)(3,4)(5,6)(7,9), (1,10)(2,3)(4,5)(6,7)(8,9)]
sage: G.gens()[0].cycle_tuples()
[(1, 8), (2, 10), (3, 4), (5, 6), (7, 9)]
}}}
But in the code in the patch we have
{{{
1357 a, b = g.cycle_tuples()[0]
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10976#comment:28>
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