Bug in order of the trivial permutation

[laurentbartholdi]

A border case for order is not well handled:

julia> Permutation(Int[])
()

julia> order(ans)
ERROR: BoundsError: attempt to access 0-element BitVector at index [1]
Stacktrace:
 [1] throw_boundserror(A::BitVector, I::Tuple{Int64})
   @ Base ./abstractarray.jl:734
 [2] checkbounds
   @ Permutations ./abstractarray.jl:699 [inlined]
 [3] setindex!
   @ Permutations ./bitarray.jl:701 [inlined]
 [4] cycles(p::Permutation)
   @ Permutations ~/.julia/packages/Permutations/zIubD/src/Permutations.jl:205
 [5] order(p::Permutation)
   @ Permutations ~/.julia/packages/Permutations/zIubD/src/Permutations.jl:299
 [6] top-level scope
   @ REPL[15]:1

[laurentbartholdi]

Not a bug, but it would make sense to add a isone method to detect triviality.

[scheinerman]

Thanks @laurentbartholdi . For the first item you mentioned, I should have order return 1.

For the second comment, are you proposing that isone(p::Permutation) should return true exactly when p is an identity permutation? That would be easily done, but just want to be clear on your suggestion.

[laurentbartholdi]

Yes, exactly! a permutation p can be multiplied with another one, and isone(p) precisely when p*q=q, so it makes perfect sense to have the identity permutation satisfy isone. Also isone(p) if and only if isone(matrix(p)).

[scheinerman]

Thanks again. Changes implemented and should be visible soon as version 0.4.18. Do you think it would make sense to also add a one method? That is one(p) would return the identity permutation of the same length as p? Not sure this is needed.

[scheinerman]

Having a tad of trouble registering ...

[scheinerman]

Having a tad of trouble registering ...

Problem solved. New version is registered.