Perm sign

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perm_sign
Computes the sign of a permutation

Other toolboxes required none
Related functions perm_inv
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.

perm_sign is a function that computes the sign of a permutation. The output of the function is either 1, indicating the permutation is even, or -1, indicating the permutation is odd.

Syntax

  • SGN = perm_sign(PERM)

Argument descriptions

  • PERM: A vector containing a permutation of the integers 1, 2, ..., n.

Examples

Small examples

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

Source code

Click on "expand" to the right to view the MATLAB source code for this function.