sfuncont.m

数字通信第四版原书的例程

function  [sys, x0] = sfuncont(t,x,u,flag)
%SFUNCONT An example S-function for continuous systems.
%	This M-file is designed to be used as a template for other
%	S-functions. Right now it acts as an integrator. This template
%	is an example of a continuous system with no discrete components.
%	That is, it makes no use of FLAG==4 or FLAG==2.
%
%	Copyright (c) 1990-94 by The MathWorks, Inc.
%	Ned Gulley 8-11-92

% Uncomment the following two lines to show how the flags are called.
% dispString=['flag = ' num2str(flag) ' at time = ' num2str(t)];
% disp(dispString)

if abs(flag) == 1,
  % The FLAG==1 branch is at the top of the file for efficiency, since
  % the S-function will be called with FLAG==1 very frequently.
  % If FLAG==1, then SIMULINK is looking for the next state derivative, dx 
  % **** In this template system, the new derivative dx gets the input u ****
  % (SYS =) DX = U
  sys = u;

elseif flag == 3,
  % If FLAG==3, then SIMULINK wants to know what the next output is.
  % **** In this template system, y gets the current state x ****
  % (SYS =) Y = X
  sys = x;
  
elseif flag  == 0,
  % This part takes care of all initialization; it is used only once.
  % **** In this template system, there is one continuous state, one ****
  % **** input and one output.                                       ****
  % The sizes vector is six elements long, and it looks like this:
  % sizes(1) = number of continuous states
  sizes(1) = 1;
  % sizes(2) = number of discrete states
  sizes(2) = 0;
  % sizes(3) = number of system outputs (length of output y)
  sizes(3) = 1;
  % sizes(4) = number of system inputs (length of input u)
  sizes(4) = 1;
  % sizes(5) = number of discontinuous roots; unused feature, set to zero
  sizes(5) = 0;
  % sizes(6) = direct feedthrough flag; used to detect algebraic loops.
  % Set sizes(6) to 1 if the output y depends directly on the input u.
  % Otherwise, it should be set to 0.
  sizes(6) = 0;
  % Set the initial conditions on the states
  x0 = 0;
  % (SYS = ) SIZES = [1 0 1 1 0 0]';
  sys = sizes';

else 
  % Flags not considered here are treated as unimportant.
  % Notice that since there are no discrete states in this system,
  % there is no need to deal with FLAG==2 or FLAG==4.
  % Output is set to [].
  sys = [];

end     % if abs(flag) == ...