题目:编写 S-函数实现输出对输入的单位延迟,即 y( k+1) = u(k)。
解:单位延迟系统的状态方程可以表述为:x(k+1)=u(k),y(k+1)=x(k+1).
s-function的代码具体如下所示:
function [sys,x0,str,ts,simStateCompliance] = sfun_unitdelay(t,x,u,flag)
switch flag,
case 0,
[sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes;
case 1,
sys=mdlDerivatives(t,x,u);
case 2,
sys=mdlUpdate(t,x,u);
case 3,
sys=mdlOutputs(t,x,u);
case 4,
sys=mdlGetTimeOfNextVarHit(t,x,u);
case 9,
sys=mdlTerminate(t,x,u);
otherwise
DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));
end
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates = 0;
sizes.NumDiscStates = 1;
sizes.NumOutputs = 1;
sizes.NumInputs = 1;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1; % at least one sample ti