Undefined function 'step' for input arguments of type 'double'

Hi,here are the codes.

w=[0.5:0.1:1,2];tt=0.4
figure(1)
hold on
for wn=w
num=[2*tt*wn,wn.^2];
den=[1,2*tt*wn,wn.^2];
step(num,den)
end
hold off

When I try to run it,I get the error Undefined function 'step' for input arguments of type 'double'.How can I do? Thank you!

[EDITED, Jan, please format your code - Thanks]

Answer 1

[Azzi Abdelmalek]

 Are you sure you have a control toolbox? type

which step

[Image Analyst]

And type ver:

>> ver

Tell us what shows up in your command window. What do you think step is supposed to do? Something in the Control System Toolbox, or something else?

[Walter Roberson]

step() is also used by the Computer Vision Toolbox, but I would say Control System is much more likely the intended application here.