Matrix form Y=Xb+8 k1 8 1Ⅹ 2,b ⅩMatrix form: 11 1 0 1 1 12 2 1 2 1 1 1 , , , 1 k k n n kn k n X X b Y X X b Y X X b    = +                       = = = =                         Y Xb ε Y X b ε