MATLAB: I have a problem. Please help!

Question

Hello everyone,

I have a problem with feedback function. When I puts these commands:

syms s
W=16/((s+1)*(s+2)*(s+3))
G=feedback(W,1)

I get these error message:

Error using feedback (line 71)
Not enough input arguments.

Please help!

Thanks in advance.

Answer 1

The arguments to feedback have to be ‘system’ objects created by tf, zpk, and related functions.

You also have to define them correctly. Your ‘W’ system for example must be defined using the tf function:

W = tf(16, [1 6 11 6]);

so you can use it in feedback.

The system you want to create becomes:

W = tf(16, [1 6 11 6])
V = tf(1, 1)
G = feedback(W,V)
W =
              16
    ----------------------
    s^3 + 6 s^2 + 11 s + 6
Continuous-time transfer function.
V =
    1
Static gain.
G =
              16
    -----------------------
    s^3 + 6 s^2 + 11 s + 22
Continuous-time transfer function.