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function [sys,x0,str,ts] = sfuntmpl(t,x,u,flag) 
%SFUNTMPL General M-file S-function template 
%   With M-file S-functions, you can define you own ordinary differential 
%   equations (ODEs), discrete system equations, and/or just about 
%   any type of algorithm to be used within a Simulink block diagram. 
% 
%   The general form of an M-File S-function syntax is: 
%       [SYS,X0,STR,TS] = SFUNC(T,X,U,FLAG,P1,...,Pn) 
% 
%   What is returned by SFUNC at a given point in time, T, depends on the 
%   value of the FLAG, the current state vector, X, and the current 
%   input vector, U. 
% 
%   FLAG   RESULT             DESCRIPTION 
%   -----  ------             -------------------------------------------- 
%   0      [SIZES,X0,STR,TS]  Initialization, return system sizes in SYS, 
%                             initial state in X0, state ordering strings 
%                             in STR, and sample times in TS. 
%   1      DX                 Return continuous state derivatives in SYS. 
%   2      DS                 Update discrete states SYS = X(n+1) 
%   3      Y                  Return outputs in SYS. 
%   4      TNEXT              Return next time hit for variable step sample 
%                             time in SYS. 
%   5                         Reserved for future (root finding). 
%   9      []                 Termination, perform any cleanup SYS=[]. 
% 
% 
%   The state vectors, X and X0 consists of continuous states followed 
%   by discrete states. 
% 
%   Optional parameters, P1,...,Pn can be provided to the S-function and 
%   used during any FLAG operation. 
% 
%   When SFUNC is called with FLAG = 0, the following information 
%   should be returned: 
% 
%      SYS(1) = Number of continuous states. 
%      SYS(2) = Number of discrete states. 
%      SYS(3) = Number of outputs. 
%      SYS(4) = Number of inputs. 
%               Any of the first four elements in SYS can be specified 
%               as -1 indicating that they are dynamically sized. The 
%               actual length for all other flags will be equal to the 
%               length of the input, U. 
%      SYS(5) = Reserved for root finding. Must be zero. 
%      SYS(6) = Direct feedthrough flag (1=yes, 0=no). The s-function 
%               has direct feedthrough if U is used during the FLAG=3 
%               call. Setting this to 0 is akin to making a promise that 
%               U will not be used during FLAG=3. If you break the promise 
%               then unpredictable results will occur. 
%      SYS(7) = Number of sample times. This is the number of rows in TS. 
% 
% 
%      X0     = Initial state conditions or [] if no states. 
% 
%      STR    = State ordering strings which is generally specified as []. 
% 
%      TS     = An m-by-2 matrix containing the sample time 
%               (period, offset) information. Where m = number of sample 
%               times. The ordering of the sample times must be: 
% 
%               TS = [0      0,      : Continuous sample time. 
%                     0      1,      : Continuous, but fixed in minor step 
%                                      sample time. 
%                     PERIOD OFFSET, : Discrete sample time where 
%                                      PERIOD > 0 & OFFSET < PERIOD. 
%                     -2     0];     : Variable step discrete sample time 
%                                      where FLAG=4 is used to get time of 
%                                      next hit. 
% 
%               There can be more than one sample time providing 
%               they are ordered such that they are monotonically 
%               increasing. Only the needed sample times should be 
%               specified in TS. When specifying than one 
%               sample time, you must check for sample hits explicitly by 
%               seeing if 
%                  abs(round((T-OFFSET)/PERIOD) - (T-OFFSET)/PERIOD) 
%               is within a specified tolerance, generally 1e-8. This 
%               tolerance is dependent upon your model's sampling times 
%               and simulation time. 
% 
%               You can also specify that the sample time of the S-function 
%               is inherited from the driving block. For functions which 
%               change during minor steps, this is done by 
%               specifying SYS(7) = 1 and TS = [-1 0]. For functions which 
%               are held during minor steps, this is done by specifying 
%               SYS(7) = 1 and TS = [-1 1]. 
 
%   Copyright 1990-2002 The MathWorks, Inc. 
%   $Revision: 1.18 $ 
 
% 
% The following outlines the general structure of an S-function. 
% 
switch flag, 
 
  %%%%%%%%%%%%%%%%%% 
  % Initialization % 
  %%%%%%%%%%%%%%%%%% 
  case 0, 
    [sys,x0,str,ts]=mdlInitializeSizes; 
 
  %%%%%%%%%%%%%%% 
  % Derivatives % 
  %%%%%%%%%%%%%%% 
  case 1, 
    sys=mdlDerivatives(t,x,u); 
 
  %%%%%%%%%% 
  % Update % 
  %%%%%%%%%% 
  case 2, 
    sys=mdlUpdate(t,x,u); 
 
  %%%%%%%%%%% 
  % Outputs % 
  %%%%%%%%%%% 
  case 3, 
    sys=mdlOutputs(t,x,u); 
 
  %%%%%%%%%%%%%%%%%%%%%%% 
  % GetTimeOfNextVarHit % 
  %%%%%%%%%%%%%%%%%%%%%%% 
  case 4, 
    sys=mdlGetTimeOfNextVarHit(t,x,u); 
 
  %%%%%%%%%%%%% 
  % Terminate % 
  %%%%%%%%%%%%% 
  case 9, 
    sys=mdlTerminate(t,x,u); 
 
  %%%%%%%%%%%%%%%%%%%% 
  % Unexpected flags % 
  %%%%%%%%%%%%%%%%%%%% 
  otherwise 
    error(['Unhandled flag = ',num2str(flag)]); 
 
end 
 
% end sfuntmpl 
 
% 
%============================================================================= 
% mdlInitializeSizes 
% Return the sizes, initial conditions, and sample times for the S-function. 
%============================================================================= 
% 
function [sys,x0,str,ts]=mdlInitializeSizes 
 
% 
% call simsizes for a sizes structure, fill it in and convert it to a 
% sizes array. 
% 
% Note that in this example, the values are hard coded.  This is not a 
% recommended practice as the characteristics of the block are typically 
% defined by the S-function parameters. 
% 
sizes = simsizes; 
 
sizes.NumContStates  = 2; 
sizes.NumDiscStates  = 0; 
sizes.NumOutputs     = 2; 
sizes.NumInputs      = 2; 
sizes.DirFeedthrough = 1; 
sizes.NumSampleTimes = 1;   % at least one sample time is needed 
 
sys = simsizes(sizes); 
 
% 
% initialize the initial conditions 
% 
x0  = [0]; 
 
% 
% str is always an empty matrix 
% 
str = []; 
 
% 
% initialize the array of sample times 
% 
ts  = [0 0]; 
 
% end mdlInitializeSizes 
 
% 
%============================================================================= 
% mdlDerivatives 
% Return the derivatives for the continuous states. 
%============================================================================= 
% 
function sys=mdlDerivatives(t,x,u) 
mx=1/25; 
bx=0.1; 
my=1/25; 
by=0.1; 
sys(1)=(u(1)-bx*x(1)-0.05*sign(x(1)))/mx; 
sys(2)=(u(2)-by*x(2)-0.05*sign(x(1)))/my; 
% end mdlDerivatives 
 
% 
%============================================================================= 
% mdlUpdate 
% Handle discrete state updates, sample time hits, and major time step 
% requirements. 
%============================================================================= 
% 
function sys=mdlUpdate(t,x,u) 
 
sys = []; 
 
% end mdlUpdate 
 
% 
%============================================================================= 
% mdlOutputs 
% Return the block outputs. 
%============================================================================= 
% 
function sys=mdlOutputs(t,x,u) 
 
sys=x; 
% end mdlOutputs 
 
% 
%============================================================================= 
% mdlGetTimeOfNextVarHit 
% Return the time of the next hit for this block.  Note that the result is 
% absolute time.  Note that this function is only used when you specify a 
% variable discrete-time sample time [-2 0] in the sample time array in 
% mdlInitializeSizes. 
%============================================================================= 
% 
function sys=mdlGetTimeOfNextVarHit(t,x,u) 
 
sampleTime = 1;    %  Example, set the next hit to be one second later. 
sys = t + sampleTime; 
 
% end mdlGetTimeOfNextVarHit 
 
% 
%============================================================================= 
% mdlTerminate 
% Perform any end of simulation tasks. 
%============================================================================= 
% 
function sys=mdlTerminate(t,x,u) 
 
sys = []; 
 
% end mdlTerminate