Error in MATLAB - Troubleshooting Guide

[blazin247nc]

[MATLAB] -- Getting Error

Code:

% Define variables for wn and z
wn = 5;
z1 = 0; z2 = 0.2; z3 = 0.9; z4 = 1; z5 = 2; z6 = 30;

% Define transfer functions
num = [wn^2];
den1 = [1, 2*z1*wn, wn^2];
den2 = [1, 2*z2*wn, wn^2];
den3 = [1, 2*z3*wn, wn^2];
den4 = [1, 2*z4*wn, wn^2];
den5 = [1, 2*z5*wn, wn^2];
den6 = [1, 2*z6*wn, wn^2];
tf_1 = tf(num, den1);
tf_2 = tf(num, den2);
tf_3 = tf(num, den3);
tf_4 = tf(num, den4);
tf_5 = tf(num, den5);
tf_6 = tf(num, den6);

% Create plots for step response

step(tf_1)
step(tf_2)
step(tf_3)
step(tf_4)
step(tf_5)
step(tf_6)


I am getting the error:

? Undefined function or method 'tf' for input arguments of type 'double'.

Error in ==> HW9_2 at 13
tf_1 = tf(num, den1);

Any ideas why?

 

[Choppy]

Have you created a function for tf?