
 The identity matrix :

              1  0  0       
       mID =  0  1  0          
              0  0  1        

 If you swap the row 1 and the row 3 of the identity matrix :

              0  0  1    > old row 3
       mID =  0  1  0           
              1  0  0    > old row 1

 And now if you multiply this matrix, 
 by a matrix mA for example :
    
              1  1  1       
        mA =  2  2  2          
              3  3  3                      

 the rows of the matrix mA are also swapped.
     
              3  3   3                      
  mID * mA =  2  2   2         
              1  1   1