Unexpected behavior for a system defined using zpk #1067
Description
I been scratching my head about whats going on with a very simple system.
Defining the system using tf yields results as expected. But defining the system through zpk does not.
Description
I intend to define the next system:
G(s) = K
---------------
(s+2)*(s+2/3)
With K adjusted for a ts=1 second. Very straight forward.
Reproduction
This is my code for zpk:
import control as ct
import numpy as np
import matplotlib.pyplot as plt
K = 10.314
G = ct.zpk([], [-2, -2/3], K)
T = ct.feedback(G)
ct.step_response(T).plot()
ct.step_info(T)
{'RiseTime': np.float64(0.0),
'SettlingTime': nan,
'SettlingMin': np.float64(-4.959514534383556e+52),
'SettlingMax': np.float64(8.010508330340013e+51),
'Overshoot': np.float64(9.04605979182796e+53),
'Undershoot': np.float64(5.600651440127666e+54),
'Peak': np.float64(4.959514534383556e+52),
'PeakTime': np.float64(5.180816459236604),
'SteadyStateValue': np.float64(0.8855245835956728)}
The result is not as expected. While defining the system through tf:
I = ct.tf([K], [1, 8/3, 4/3])
V = ct.feedback(I)
ct.step_response(V).plot()
ct.step_info(V)
{'RiseTime': np.float64(0.4186518350898263),
'SettlingTime': np.float64(2.5119110105389577),
'SettlingMin': np.float64(0.8127467853231765),
'SettlingMax': np.float64(1.118911703975943),
'Overshoot': np.float64(26.35435717033743),
'Undershoot': 0,
'Peak': np.float64(1.118911703975943),
'PeakTime': np.float64(0.9942981083383374),
'SteadyStateValue': np.float64(0.8855347207912633)}
Outputting both system definitions reveals they're the same. The transfer function is exactly the same. But I don't know what may be going on with the transfer object defined with zpk.
System info
I've installed the control package in a clean conda enviroment and using a jupyter notebook through VSCode.
Conda:
conda version : 23.1.0
conda-build version : 3.22.0
python version : 3.9.13.final.0
virtual packages : __archspec=1=x86_64__win=0=0
platform : win-64