中文说明：关于滑模控制的程序比较少，这是典型的几个程序，对于搞滑模控制的有重要的参考价值，3－1基于趋近律的离散滑模控制（关于二阶系统）
English Description：
There are few programs about sliding mode control. These are typical programs, which have important reference value for sliding mode control. 3-1 discrete sliding mode control based on reaching law (about second-order system)