The parity should be zero if the vector is not a true permutation, i.e.
julia> sign([3, 4, 5, 4, 1])
-1
would at least be misleading. Could result in an ERROR, but I still
suggest to return 0.
On Tuesday, February 10, 2015 at 3:24:19 PM UTC+1, Stefan Karpinski wrote:
>
> Thanks for the code – would you be willing to contribute it under the MIT
> license?
>
> On Tue, Feb 10, 2015 at 9:21 AM, Dawid Crivelli <[email protected]
> <javascript:>> wrote:
>
>> I have a short code for checking the sign of a permutation for personal
>> use. It's O(L^2) where L is the length of the permutation vector, but it's
>> perfectly fine for L in the few tens range.
>>
>> function sign{T<:Integer}(perm::AbstractVector{T})
>> L = length(perm)
>> crosses = 0
>> for i = 1:L
>> for j = i+1 : L
>> crosses += perm[j] < perm[i]
>> end
>> end
>> return iseven(crosses) ? 1 : -1
>> end
>>
>>
>>
>
