DEFINITION 5 Matrices 矩阵 The identity matrix of order n is the n X n matrix I i &,I, where al if i=j and 8-0 if j. Hence 01 了 00M a t r i c e s 矩 阵 DEFINITION 5. The identity matrix of order n is the n × n matrix In = [ ], where =1 if i = j and = 0 if i ≠ j. Hence