DEFINITION 2 Matrices 矩阵 The ith row ofa is the 1 x n R 12 Let A= matrix ail, aj,., ain. The a. a.a. jth column of a is then X1 matrix The (i, j)th element or entry of A is the element aii that is, the number in the ith row and jth column ofA. A convenient shorthand notation for expressing the matrix A is to write A=ail, which indicates that a is the matrix with its (i, j)th element equal to a iM a t r i c e s 矩 阵 DEFINITION 2. Let The (i, j)th element or entry of A is the element aij, that is, the number in the ith row and jth column of A. A convenient shorthand notation for expressing the matrix A is to write A = [aij], which indicates that A is the matrix with its (i, j)th element equal to aij. The ith row of A is the 1 × n matrix [ai1, ai2, …, ain]. The jth column of A is the n × 1 matrix