How can i fix that? And are there any error in my code? thank. "X0 returned by MATLAB S-function 'mppt1' in 'solar/S-Function' must be a vector of length 4"

function [sys,x0,str,ts,simStateCompliance] = mppt1(t,x,u,flag)

%SFUNDSC2 Example unit delay MATLAB File S-function

% The MATLAB file S-function is an example of how to implement a unit

% delay.

%

% See sfuntmpl.m for a general S-function template.

%

% See also SFUNTMPL.

% Copyright 1990-2009 The MathWorks, Inc.

switch flag,

%%%%%%%%%%%%%%%%%%

% Initialization %V

%%%%%%%%%%%%%%%%%%

case 0,

[sys,x0,str,ts,simStateCompliance] = mdlInitializeSizes;

%%%%%%%%%%

% Update %

%%%%%%%%%%

case 2,

sys = mdlUpdate(t,x,u);

%%%%%%%%%%

% Output %

%%%%%%%%%%

case 3,

sys = mdlOutputs(t,x,u);

%%%%%%%%%%%%%

% Terminate %

%%%%%%%%%%%%%

case 9,

sys = [];

otherwise

DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));

end

%end sfundsc2

%

%=============================================================================

% mdlInitializeSizes

% Return the sizes, initial conditions, and sample times for the S-function.

%=============================================================================

%

function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes

sizes = simsizes;

sizes.NumContStates = 0;

sizes.NumDiscStates = 4;

sizes.NumOutputs = 1;

sizes.NumInputs = 1;

sizes.DirFeedthrough = 1;

sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

%initial conditions

x0=[0;0;0;0];

str = [];

ts = [0.01 0]; % Sample period of 0.1 seconds (10Hz)

% speicfy that the simState for this s-function is same as the default

simStateCompliance = 'DefaultSimState';

% end mdlInitializeSizes

%

%=======================================================================

% mdlUpdate

% Handle discrete state updates, sample time hits, and major time step

% requirements.

%=======================================================================

%

function sys = mdlUpdate(t,x,u)

x(1)=u;

if x(1)>x(2)

x(2)=x(1);

x(3)=x(4);

x(4)=t(3)+0.01;

else

x(3)=x(4);

x(4)=x(3)-0.01;

end

sys = x;

%end mdlUpdate

%

%=======================================================================

% mdlOutputs

% Return the output vector for the S-function

%=======================================================================

%

function sys=mdlOutputs(t,x,u)

sys = x(4);

%end mdlOutputs

Answer 1

[Shubham]

Hi @Do An

The error message indicates that the initial condition vector x0 must have a length of 4. Your code seems to be correct in that regard, as you have defined "x0" as a 4-element vector:

x0 = [0; 0; 0; 0];

However, the issue may arise from the "mdlUpdate" function. Ensure that you're updating the state vector "x" properly. As far as I understand, accessing "t(3)" doesn't make sense because "t" is a scalar representing the current time.

Try modifying the update function as:

function sys = mdlUpdate(t,x,u)
x(1) = u; % Assuming u is a scalar input
if x(1) > x(2)
    x(2) = x(1);
    x(3) = x(4);
    x(4) = t + 0.01; % Changed from t(3) to t
else
    x(3) = x(4);
    x(4) = x(3) - 0.01;
end
sys = x;    

If you are still facing issues, then try sharing the model for complete reproduction of the issue.

I hope this helps!