

 The  matrix m :

            1    1    2 
       m =  3/2  3/4  3 
            4/3  2    1/2

 If you copy all the values below the pivot
 in the identity matrix. And take the opposite.

              1    0   0        
       mID = -3/2  1   0           
             -4/3  0   1         

  If you multiply this matrix by m,  all the
  values below  the pivot will be equal to 0
             
            1   1     2 
  mID * m = 0  -3/4   0 
            0   2/3 -13/6

