Difference between revisions of "Perm sign"
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|name=perm_sign | |name=perm_sign | ||
|desc=Computes the sign of a permutation | |desc=Computes the sign of a permutation | ||
| + | |rel=[[perm_inv]] | ||
|upd=November 21, 2012 | |upd=November 21, 2012 | ||
|v=1.00 | |v=1.00 | ||
Revision as of 17:14, 21 January 2013
| perm_sign | |
| Computes the sign of a permutation | |
| Other toolboxes required | none |
|---|---|
| Related functions | perm_inv |
| 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