例1 21 B= 01 12 一 般而言 AB≠BA,即矩阵乘法不满足交换律， 但满足结合律 ABC=A(BC)=(AB)C 例1       = 0 1 0 1 0 1 A           = 1 0 0 1 2 1 B       =                 = 0 1 3 1 1 0 0 1 2 1 0 1 1 0 0 1 AB           =                = 1 0 1 0 1 0 2 1 2 0 1 1 0 0 1 1 0 0 1 2 1 BA 一般而言 AB  BA, 即矩阵乘法不满足交换律， 但满足结合律 ABC = A(BC) =(AB)C