4单位矩阵和纯量矩阵 1 0 0 0 1 0 Unit matrix:/ 0 0 IA=AL In =I 0 0 0 0 1 k 0 0 0 0 Scalar matrix:S= =k1SA=AS(3.20) 00 0 0 0 0 k4 单位矩阵和纯量矩阵 Unit matrix: Scalar matrix:             = 0 0 0 1 0 0 0 0 1 0 1 0 0    I k I k k k S =             = 0 0 0 0 0 0 0 0 0 0    IA = AI, In = I SA = AS (3.20)