MATLAB: S-function error

nonlinear discrete-time systemss-functionsimulink

hi guys when i try to use the follow s-function in a simulink blocket, i obtain this error:
Sizes vector returned by MATLAB S-function 'NARMASYSTEM' in 'NARMA/S-Function' must be a real vector consisting of integer value of length 7
This is the function code:
function [sys,x0,str,ts] = NARMASYSTEM(t,x,u,flag)
%M-file S-function for defining a discrete system.
% This S-function implements discrete equations
% Generate a discrete nonlinear system:
a1=0.2;
a2=0.1;
g1=1;
g2=0.2;%=-0.2
b1=0.3;
b2=-0.6;
switch flag,
  case 0
    [sys,x0,str,ts] = mdlInitializeSizes(a1,a2,g1,g2,b1,b2); % Initialization

    case 2
     [sys,x0,str,ts] = mdlUpdates(t,x,u,a1,a2,g1,g2,b1,b2); % Update discrete states
    case 3
      [sys,x0,str,ts] = mdlOutputs(t,x,u,a1,a2,g1,g2,b1,b2); % Calculate outputs

    case {1, 4, 9} % Unused flags
      sys = [];
    otherwise
      error(['unhandled flag = ',num2str(flag)]); % Error handling
  end
  % End of dsfunc.
%==============================================================





% Initialization
%==============================================================
function [sys,x0,str,ts] = mdlInitializeSizes(a1,a2,g1,g2,b1,b2)
% Call simsizes for a sizes structure, fill it in, and convert it 
% to a sizes array.
sizes = simsizes;
sizes.NumContStates  = 0;
sizes.NumDiscStates  = 2;
sizes.NumOutputs     = 2;
sizes.NumInputs      = 2;
sizes.DirFeedthrough = 0; % Matrix D is non-empty.
sizes.NumSampleTimes = 0.05;
sys = simsizes(sizes); 
x0  = [0 1];   % Initialize the discrete states.
str = [];          % Set str to an empty matrix.
ts  = [1 0];       % sample time: [period, offset]
% End of mdlInitializeSizes.
%==============================================================
% Update the discrete states
%==============================================================
function sys = mdlUpdates(t,x,u,a1,a2,g1,g2,b1,b2)
sys(1) =a1*x(1)*cos(x(1))+a2*(x(1)^2)/(1+x(1)^2)+g1*x(2) ;
sys(2)=b1*sin(x(1))+b2*(x(1)^3)/(2+x(1)^2)+g2*u(1)+u(2);
% End of mdlUpdate.
%==============================================================
% Calculate outputs
%==============================================================
function sys = mdlOutputs(t,x,u,a1,a2,g1,g2,b1,b2)
sys(1) =x(1);
sys(2)=x(2);
% End of mdlOutputs.

Best Answer

NumSampleTimes cannot be a fractional value. You need to change:
   sizes.NumSampleTimes = 0.05;
to:
   sizes.NumSampleTimes = 1;
Btw, if you are writing a new S-function, I would highly recommend that you consider switching to Level-2 MATLAB S-functions instead (you are writing a Level-1 MATLAB S-function). Level-1 S-functions have been deprecated for a long time and do not support a wide range of Simulink features. Support for these S-functions may also be discontinued in a future release.
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