G = tf([2, 6, 4],[1,-2,1], display_format='poly')
print(G)

G = tf([2, 6, 4],[1,-2,1], display_format='zpk')
print(G)

G = tf([2, 6, 4],[1,-2,1], dt=0.1, display_format='poly')
print(G)

G = tf([2, 6, 4],[1,-2,1], dt=0.1, display_format='zpk')
print(G)

2 s^2 + 6 s + 4
---------------
 s^2 - 2 s + 1


2 (s + 1) (s + 2)
-----------------
 (s - 1) (s - 1)


2 z^2 + 6 z + 4
---------------
 z^2 - 2 z + 1

dt = 0.1


2 (z + 1) (z + 2)
-----------------
 (z - 1) (z - 1)

dt = 0.1