教程地址：https://www.bilibili.com/video/BV1bv411C7Y7?p=1

edit sfuntmpl 命令打开官方自带的s函数例程

下面是s函数的一个模版

%S-function for continuous state equation
function [sys,x0,str,ts]=s_function(t,x,u,flag)
 
switch flag,
%Initialization 
  case 0,
    [sys,x0,str,ts]=mdlInitializeSizes;
case 1,
    sys=mdlDerivatives(t,x,u);
%Outputs
  case 3,
    sys=mdlOutputs(t,x,u);
%Unhandled flags
  case {2, 4, 9 }
    sys = [];
%Unexpected flags
  otherwise
    error(['Unhandled flag = ',num2str(flag)]);
end

%mdlInitializeSizes
function [sys,x0,str,ts]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates  = 2;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 1;
sizes.NumInputs      = 1;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 0;

sys=simsizes(sizes);
x0=[0,0];
str=[];
ts=[];

function sys=mdlDerivatives(t,x,u)

sys(1)=x(2);
%sys(2)=-(25+5*sin(t))*x(2)+(133+10*sin(t))*u;
sys(2)=-(25+10*rands(1))*x(2)+(133+30*rands(1))*u;

function sys=mdlOutputs(t,x,u)

sys(1)=x(1);