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 =
1The permutation that transposes 3 and 4 is odd:
>> perm_sign([1,2,4,3,5])
ans =
-1A 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 =
1Source code
Click on "expand" to the right to view the MATLAB source code for this function.