Difference between revisions of "Perm sign"
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| − | <tt>'''perm_sign'''</tt> is a [[List of functions|function]] that computes the [http://en.wikipedia.org/wiki/Parity_of_a_permutation sign a permutation]. The output of the function is either 1, indicating the permutation is even, or -1, indicating the permutation is odd. | + | <tt>'''perm_sign'''</tt> is a [[List of functions|function]] that computes the [http://en.wikipedia.org/wiki/Parity_of_a_permutation 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== | ==Syntax== | ||
Revision as of 16:54, 27 November 2012
| perm_sign | |
| Computes the sign of a permutation | |
| Other toolboxes required | none |
|---|---|
| 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