克罗内克( Kronecker)符号 0 l≠ 6n符号具有以下重要性质: JJ 6n=O1+62+S3=3 j克罗内克(Kronecker)符号    = 1 0  ij i  j i = j  ij 符号具有以下重要性质：  ij =  ji  ija j = ai  ii = 3  ij jk =  ik  ij ij =  ii = 3 12 21 31 13  =  , =  j a j = a  j a j = a  j a j = a  i ja j = ai , , , 1 1 2 2 3 3  ii =  11 + 22 + 33 = 3