The control package is part of the Octave Forge project.
Linear System Representation
Some very basic examples
PT1/low-pass filter step response
|Code: Creating a transfer function and plotting its response
T1=0.4; # time constant
P=tf(, [T1 1]) # create transfer function model
step(P,2) # plot step response
#add some common markers like the tangent line at the origin, which crosses lim(n->inf) f(t) at t=T1
plot ([0 T1], [0 1],"g")
plot ([T1 T1], [0 1],"k")
plot ([0 T1], [1-1/e 1-1/e],"m")
Try also bode(P)!
(a first order low-pass filter has -3db magnitude at f=1/T1)