This error occurs because the input argument of the controlSystemDesigner function is not a valid transfer function object.
The tf function creates a transfer function object, but in your example, it is missing some required arguments. A valid transfer function object requires at least two arguments: the numerator coefficients and the denominator coefficients.
To fix this error, you need to provide both the numerator and denominator coefficients as arguments to the tf function. For example, to create a transfer function with numerator 1 and denominator [1,1], you should use:
sys = tf([1], [1, 1]);
controlSystemDesigner(sys)
This will create a transfer function object sys and open it in the controlSystemDesigner app.
