MATLAB: Simulink matlab function block error

embedded matlab functionmatlab codersimulink

Hello guys,
Im trying to calculate my lqr gains online, im having some troubles with the simulation, i get the error message saying
Function output 'Kr' cannot be an mxArray in this context. Consider preinitializing the output variable with a known type.
Errors occurred during parsing of MATLAB function
Here is the code, I am trying to obtain the Kr(1,1) in this case.
    % code
function Kr = fcn(u)
%#codegen
eml.extrinsic('lqr'); 
a = 1.3629;
b = 1.2996;
Cf = 16000;
Cr = 16000;
Cr2 = 15000;
I = 2761;
l = a+b;
m = 2024.65;
w = 2e-7;
a11 = -2*(Cf+Cr)/(m*u);
a12 =(2*(b*Cr - a*Cf)/(m*u))-u;
a21 = 2*(b*Cr-a*Cf)/(I*u);
a22 = -2*(b^2*Cr+a^2*Cf)/(I*u);
b1 = 0;
b2 = 1/I;
A = [a11 a12; a21 a22];
B = [b1; b2];
Q = [0 0; 0 1];
R = [w];
Kr = lqr(A,B,Q,R);
  end

Best Answer

You need to tell the compiler what the output of lqr will look like.
Kr = zeros(1,2); % Define the output type for the extrinsic call.
Kr = lqr(A,B,Q,R);
Then you can do what you want with Kr.
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