### 2.10.5 Transform a permutation into a matrix : `permu2mat`

`permu2mat` takes as argument a permutation *p* of size *n*.

`permu2mat` returns the matrix of the permutation, that is
the matrix obtained by permuting the rows of the identity matrix of size *n*
with the permutation *p*.

Input :

`permu2mat([2,0,1])`

Output :

`[[0,0,1],[1,0,0],[0,1,0]]`