说明：  这是关于滑模控制程序设计的最后一个源代码（关于离散跟踪），如果能将这几个程序弄明白，那么设计滑模控制器应该是没有问题的了
(This is on the design of sliding mode control procedures for the last source code (on the discrete tracking), if these procedures can be understood, then the design of sliding mode controller should be no problem at all)