It seems that this is intended? The correct equivalent code is:
sage: gens = [[(2, 4)], [(1, 2)]]
sage: pg = PermutationGroup(gens=gens); pg
Permutation Group with generators [(2,4), (1,2)]
sage: pg._libgap_()
Group([ (2,4), (1,2) ])
sage: pg = PermutationGroup(gens=gens, domain={1, 2, 4}); pg
Permutation Group with generators [(2,4), (1,2)]
sage: pg._libgap_()
Group([ (2,3), (1,2) ])
Which is what's done at
https://github.com/sagemath/sage/blob/develop/src/sage/graphs/generic_graph.py#L24161-L24170.
But I'm not an expert in this part of the code.
Also, I didn't know we have a 25k lines file.
On 1/28/25 10:27 AM, 'Peter Mueller' via sage-devel wrote:
> The following code shows that subgroups of automorphism groups of graphs are
> handled wrongly:
>
> sage: g = Graph([[1, 2, 4], []])
> sage: a = g.automorphism_group()
> sage: print(a)
> Permutation Group with generators [(2,4), (1,2)]
> sage: print(a.commutator())
> Permutation Group with generators [(1,2,3)]
>
> Note that a.commutator() moves 3 though 3 is not a vertex of the graph.
> Somewhat strangely, if one defines directly a = PermutationGroup([[(2, 4)],
> [(1,
> 2)]]), then a.commutator() returns the correct subgroup.
>
> By the way, it doesn't help if the n vertices of the graph consist of the list
> [1..n]. I have a complicated example where the automorphism group is computed
> correctly, but the action of the commutator subgroup is with respect to a
> different labeling of the vertices.
>
> -- Peter Mueller
>
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