Thank you for your answers.
It's very confusing to write a right action to the left : we write g(i) and
not (i)g.
By default it should be a left action.
And its very confusing that PermutationGroup and Permutation doesn't give
the same matrix for the same permutation.
I think that Sage should be coherent with itself as much as possible, and
that it should choose the most natural convention.
Best regards,
Paul
Le lundi 15 juin 2020 17:30:33 UTC+2, David Joyner a écrit :
>
>
>
> On Mon, Jun 15, 2020 at 11:21 AM 'Paul Mercat' via sage-devel <
> sage-...@googlegroups.com <javascript:>> wrote:
>
>> Another bug with PermutationGroup:
>>
>> {{
>> g1,g2 = PermutationGroup([(1,2,3,4), (1,3,2,4)]).gens()
>> (g1*g2)(3), g1(g2(3))
>> }}
>>
>> should gives two times the same result, but it is not the case...
>> The action of the group on {1,2,3,4} is not an action !
>>
>
> Did you mean to say the action on {1,2,3,4} is not a left action?
> Some prefer right actions....
>
>
>>
>> Le lundi 15 juin 2020 16:58:18 UTC+2, Paul Mercat a écrit :
>>>
>>> Hi !
>>>
>>> Sage doesn't compute correctly the matrix of a Permutation:
>>>
>>> matrix(Permutation('(1,2,3,4)'))
>>>
>>> return a wrong answer: it returns the inverse of the correct result.
>>> The product of matrices of permutations must be equal to the matrix of
>>> the composition.
>>>
>>> If we do:
>>>
>>> PermutationGroup([(1,2,3,4)]).gens()[0].matrix()
>>>
>>> then we get the correct result.
>>>
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