function [sys,x0,str,ts] = timestwo(t,x,u,flag)
%TIMESTWO S-function whose output is two times its input.
%   This M-file illustrates how to construct an M-file S-function that
%   computes an output value based upon its input.  The output of this
%   S-function is two times the input value:
%
%     y = 2 * u;
%
%   See sfuntmpl.m for a general S-function template.
%
%   See also SFUNTMPL.
    
%   Copyright (c) 1990-1998 by The MathWorks, Inc. All Rights Reserved.
%   $Revision: 1.3 $

%
% Dispatch the flag. The switch function controls the calls to 
% S-function routines at each simulation stage of the S-function.
%
switch flag,
  %%%%%%%%%%%%%%%%%%
  % Initialization %
  %%%%%%%%%%%%%%%%%%
  % Initialize the states, sample times, and state ordering strings.
  case 0
    [sys,x0,str,ts]=mdlInitializeSizes;

  %%%%%%%%%%%
  % Outputs %
  %%%%%%%%%%%
  % Return the outputs of the S-function block.
  case 3
    sys=mdlOutputs(t,x,u);

  %%%%%%%%%%%%%%%%%%%
  % Unhandled flags %
  %%%%%%%%%%%%%%%%%%%
  % There are no termination tasks (flag=9) to be handled.
  % Also, there are no continuous or discrete states,
  % so flags 1,2, and 4 are not used, so return an emptyu
  % matrix 
  case { 1, 2, 4, 9 }
    sys=[];

  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % Unexpected flags (error handling)%
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % Return an error message for unhandled flag values.
  otherwise
    error(['Unhandled flag = ',num2str(flag)]);

end

% end timestwo

%
%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
%
function [sys,x0,str,ts] = mdlInitializeSizes()

sizes = simsizes;
sizes.NumContStates  = 0;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = -1;  % dynamically sized
sizes.NumInputs      = -1;  % dynamically sized
sizes.DirFeedthrough = 1;   % has direct feedthrough
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);
str = [];
x0  = [];
ts  = [-1 0];   % inherited sample time

% end mdlInitializeSizes

%
%=============================================================================
% mdlOutputs
% Return the output vector for the S-function
%=============================================================================
%
function sys = mdlOutputs(t,x,u)

sys = u * 2;

% end mdlOutputs

