Simulink user defined function: undefined variable or function

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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?

Accepted Answer

Walter Roberson
Walter Roberson on 11 Jun 2012
Start the routine with
xdot = zeros(1, n+2);
  2 Comments
Martijn
Martijn on 11 Jun 2012
Thank you, the function variable are not allowed to change size to be able to generate code.
Sumukh Bharadwaj
Sumukh Bharadwaj on 21 Mar 2018
Hi,
I'm facing the same problem! "Undefined function and first assignment........
How did you overcome it?

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