User`s guide

Examples of M-File S-Functions
2-9
Example - Continuous State S-Function
Simulink includes a function called csfunc.m, which is an example of a
continuous state system modeled in an S-function. Here is the code for the
M-file S-function:
function [sys,x0,str,ts] = csfunc(t,x,u,flag)
% CSFUNC An example M-file S-function for defining a system of
% continuous state equations:
% x' = Ax + Bu
% y = Cx + Du
%
% Generate a continuous linear system:
A=[−0.09 −0.01
1 0];
B=[ 1 −7
0 −2];
C=[ 0 2
1 −5];
D=[−3 0
1 0];
%
% Dispatch the flag.
%
switch flag,
case 0
[sys,x0,str,ts]=mdlInitializeSizes(A,B,C,D); % Initialization
case 1
sys = mdlDerivatives(t,x,u,A,B,C,D); % Calculate derivatives
case 3
sys = mdlOutputs(t,x,u,A,B,C,D); % Calculate outputs
case { 2, 4, 9 } % Unused flags
sys = [];
otherwise
error(['Unhandled flag = ',num2str(flag)]); % Error handling
end
% End of csfunc.