随机过程第五版（刘次华）第四章课后题4.2,4.6,4.7，4.8，其中关于24个季度的销售记录的转移概率等(The fifth edition of the random process (Liu Cihua) Chapter 4 after class questions 4.2, 4.6, 4.7, 4.8, including the transfer probability of sales records for 24 quarters, etc.)