|Computes the sign of a permutation|
|Other toolboxes required||none|
|Function category||Helper functions|
|This is a helper function that only exists to aid other functions in QETLAB. If you are an end-user of QETLAB, you likely will never have a reason to use this function.|
- SGN = perm_sign(PERM)
- PERM: A vector containing a permutation of the integers 1, 2, ..., n.
The identity permutation is even:
>> perm_sign(1:4) ans = 1
The permutation that transposes 3 and 4 is odd:
>> perm_sign([1,2,4,3,5]) ans = -1
A large example
This function has no trouble with large permutations. The following code determines the sign of a random permutation of 1:1000000 in under 1/2 of a second on a standard desktop computer:
>> perm_sign(randperm(1000000)) ans = 1
Click on "expand" to the right to view the MATLAB source code for this function.