Dumb question about step

[Giuseppe Marullo]

Hi all,
I am trying to use octave to run a simulation of a PID system:

http://www.engin.umich.edu/class/ctms/matlab42/pid/pid.htm

This is the first one:

num=1;
den=[1 10 20];
step(num,den)
I get this output:
error: step: sys must be a system data structure.
error: evaluating if command near line 64, column 3
error: called from `step' in file `C:\Program
Files\Octave\share\octave\3.0.0\m\control\base\step.m'
Does not work in octave, while in matlab I get a nice graph.
I need to run simple stuff, but I need complete compatibility with
matlab(welcome to the club, I guess).
Thanks in advance,
Giuseppe
PS: I  am a total n00b at matlab