Index exceeds array bounds; transfer function model.

I'm modelling the dynamics of an inverted pendulum system. Here's my code:

m=0.1283; M=0.5; I=0.0107; g=9.81; L=0.5;

s=tf('s')

s =
 
  s
 
Continuous-time transfer function.

J=m*(L^2)/4+I;
H=M+m;
G=m*g*L/2;
E=m*L/2;
P=J*H-E^2;
format short

sys=1/(P/E*s^2-(E^2+P)*G/(J*E))

sys =
 
          1
  ------------------
  0.3346 s^2 - 6.164
 
Continuous-time transfer function.

Which [produced the expected result here, but] yields the following error [in my computer]:

Index exceeds array bounds.

Error in sym/subsref (line 859)

R_tilde = builtin('subsref',L_tilde,Idx);

Error in modelo_dominio_s_sin_friccion (line 5)

s=tf('s')

How can I fix it? I'm not sure why there appears to be an error with s=tf('s') when it appears exactly like that in the 'tf' documentation.

[Harshavardhan]

Hi @an Electrical Engineering Student

The error you're encountering seems to be related to the s=tf('s') line in your code. Ensure that you have the Control System Toolbox and that it is correctly set up.

If the problem persists, try restarting or updating MATLAB.

Hope this helps.

[Walter Roberson]

Indeed, this error is due to having an existing variable named tf

[Sam Chak]

Let's test out @Walter Roberson's hypothesis...

%% ----- assign an existing variable named 'tf' -----
tf = 2;             % Test 1
% syms tf           % Test 2
% tf = @(x) 2*x;    % Test 3
%  --------------------------------------------------

m=0.1283; M=0.5; I=0.0107; g=9.81; L=0.5;

s=tf('s')

Index exceeds the number of array elements. Index must not exceed 1.

tf appears to be both a function and a variable. If this is unintentional, use 'clear tf' to remove the variable 'tf' from the workspace.

J=m*(L^2)/4+I;
H=M+m;
G=m*g*L/2;
E=m*L/2;
P=J*H-E^2;
format short

sys=1/(P/E*s^2-(E^2+P)*G/(J*E))