Simulink user defined function: undefined variable or function

Dear all,

When using a user defined Matlab function in Simulink, with the following structure:

function xdot = fcn(x,u)
%VEHICLE PROPERTIES (removed here)

%%Dea
xdot(1)=V*cos(x(1));
xdot(2)=V*sin(x(1));
xdot(3)=V*1/l(1)*tan(u);
xdot(4)=-xdot(3)-V/l(2)*sin(x(4))-xdot(3)*(c(1)/l(2))*cos(x(4));
V(1)=V;

for k=2:n-1
ratep=xdot(3)+sum(xdot(4:k+2)); %yaw-rate precessing unit
V(k)=V(k-1)*cos(x(k+2))-ratep*c(k-1)*sin(x(k+2)); %velocity precessing unit
xdot(k+3)=-ratep-V(k)/l(k+1)*sin(x(k+3))-ratep*(c(k)/l(k+1))*cos(x(k+3));
end
end

I get the errors: Undefined function or variable 'xdot'. The first assignment to a local variable determines its class.

As you can see, I want to assign a value to xdot, so I do not understand where the error comes from. Can anyone help?

Answer 1

[Walter Roberson]

Start the routine with

xdot = zeros(1, n+2);

[Martijn]

Thank you, the function variable are not allowed to change size to be able to generate code.

[Sumukh Bharadwaj]

Hi,

I'm facing the same problem! "Undefined function and first assignment........

 How did you overcome it?