说明：  S函数即系统函数System Function的意思，为什么要使用S函数呢？是因为在研究中，有时需要用到复杂的算法设计等，而这些算法因为其复杂性不适合用普通的Simulink模块来搭建，即matlab所提供的Simulink模块不能满足用户的需求，需要用编程的形式设计出S函数模块，将其嵌入到系统中。如果恰当地使用S函数，理论上，可以在Simulink下对任意复杂的系统进行仿真。
(S function means system function. Why use s function? Because in the research, sometimes we need to use complex algorithm design, and these algorithms are not suitable to use ordinary Simulink module because of their complexity, that is, the Simulink module provided by Matlab can not meet the needs of users, so we need to design s function module in the form of programming, and embed it into the system. If s function is used properly, any complex system can be simulated under Simulink.)