I just had a quick look at it, and the following looks downright scary:
+ For backward compatibility, if a permutation group element
+ acts on the integers `\{1,\ldots,n\}` or a subset thereof,
+ the columns are considered as being numbered from `1`::
+
+ sage: G = PermutationGroup(['(1,2,3)(4,5)', '(1,2,3,4,5)'])
+ sage: sigma, tau = G.gens()
+ sage: sigma
+ (1,2,3)(4,5)
+ sage: M = copy(N)
+ sage: M.permute_columns(sigma)
+ sage: M
+ [1 0 1 0 0]
+ [2 2 0 0 0]
+ [0 3 0 0 3]
+ [0 0 0 4 4]
+ [0 0 0 5 0]
note that there is an unpleasant ambiguity here:
namely, if, say in this example you take
G = PermutationGroup(['(1,2,3)'])
how one could tell whether it is meant to permute stuff in [0..2], or in
[1..3] ?
Do you mean that one must write G = PermutationGroup(['(0),(1,2,3)']) for
the latter?
Dima
On Wednesday, September 3, 2014 2:46:25 PM UTC+1, Nicolas M. Thiéry wrote:
>
> Dear Sage devs,
>
> From the description of ticket #16577:
>
> Permutation groups used to only handle permutations of 1,..n, and the
> methods permute_rows and friends of matrices coped with this with an
> ugly and potentially confusing shift by 1. After this ticket,
> permutation of 0,...,n-1 are accepted and handled as can be
> expected. For permutations of 1..n and subsets thereof, the behavior
> is unchanged for backward compatibility.
>
> This ticket also includes the following changes:
>
> A rewrite of the documentation
> New documentation on a related method
> Code refactorization to avoid some duplication
> The implementation of M.permute_rows_and_columns(sigma)
>
> The ticket has been reviewed by Karl and is ready to go. This is just
> a final call in case someone would have some more opinion about it.
>
> Speak now or forever hold your peace :-)
>
> Cheers,
> Nicolas
> --
> Nicolas M. Thiéry "Isil" <nth...@users.sf.net <javascript:>>
> http://Nicolas.Thiery.name/
>
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