Hello,

I am following a book example. I noticed that when I plot the Nyquist plot for a stated open-loop transfer function L(s), the dimensions and shape of the plots are different depending on how I define the denominator cofactor between (s/10 + 1) vs. (s + 10). Shouldn't this be treated as equivalent? Also note that for either versions, the dimension (magnitude radius) differs from what the book shows as per the following screenshot from the textbook (at w = 0, u = 100, whereas for the script versions, they are 15 and 10, respectively).

Plot results are for different cofactor version used (the one on the left is for (s/10 + 1) and the one on the right is for (s + 10)) :

Here is the test script for the open-loop transfer function L(s) = Gc(s)G(s):

import matplotlib.pyplot as plt
import control as ct

Gc = ct.TransferFunction([100], [1, 1]) # 100 / (s + 1)
G = ct.TransferFunction([1], [0.1, 1])  # 1 / (s/10 + 1)
# G = ct.TransferFunction([1], [1, 10])   # 1 / (s + 10) -- alternate 'G'

Open_Loop = ct.series(Gc, G, name='Open_Loop')
F_sys = ct.TransferFunction(Open_Loop)

plt.style.use('dark_background')
ct.nyquist_plot([F_sys])

# Increase size of red marker
ax = plt.gca()
ax.plot(-1, 0, 'x', color = 'red', markersize=7)

plt.show()

Can someone please advise why there are differences between the plots obtained using the script using both cofactors with respect to the result obtained in the textbook.

Thank you.