# Perm inv

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 Other toolboxes required perm_inv Computes the inverse of a permutation none perm_sign 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_inv is a function that computes the inverse of a permutation.

## Syntax

• PI = perm_inv(PERM)

## Argument descriptions

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

## Examples

### Small examples

The identity permutation is its own inverse:

```>> perm_inv(1:4)

ans =

1     2     3     4```

To compute the inverse of the permutation on this MathWorld page, we can use the following line of code:

```>> perm_inv([3,8,5,10,9,4,6,1,7,2])

ans =

8    10     1     6     3     7     9     2     5     4```

## Source code

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

1. `%%  PERM_INV    Computes the inverse of a permutation`
2. `%   This function has one required argument:`
3. `%     PERM: a permutation vector`
4. `%`
5. `%   PI = perm_inv(PERM) is the inverse permutation of PERM.`
6. `%`
7. `%   URL: http://www.qetlab.com/perm_inv`
8. ` `
9. `%   requires: nothing`
10. `%   author: Nathaniel Johnston (nathaniel@njohnston.ca)`
11. `%   package: QETLAB`
12. `%   last updated: November 28, 2012`
13. ` `
14. `function res = perm_inv(perm)`
15. ` `
16. `[~,res] = sort(perm);`