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Bode plots use Hz instead of rad/sec in MATLAB compatibility mode #373
Description
Hi everyone,
When I try the bode function from the control.matlab library to plot the Bode of a simple function (H(s)=1/(s+1)) I'm getting the wrong angular frequencies (shifted one decade). In other words, the break frequency is at 0.1 rad/s instead of 1.0 rad/s (see image). I'm not sure if this is an issue or I'm just doing something wrong. Could you please help me with this problem.
My system is a macOS Catalina 10.15.3 and I'm using Python 3.7.5.
import numpy as np
import control.matlab as ml
import matplotlib.pyplot as plt
num = np.array([1])
den = np.array([1, 1])
G = ml.tf(num, den)
print(G)
mag, phase, freq = ml.bode(G)
plt.show()
Thank you
Activity
murrayrm commentedon Feb 17, 2020
The units for frequency are in Hertz, not rad/sec. 1 rad/sec = 1/(2*pi) Hz = 0.16, which is where the breakpoint is (easiest to see as the point where the phase crosses 45 degrees).
It looks like this is a bug in the way that defaults are set up for the MATLAB compatibility module, which sets
bode.Hz = True. Can't remember if this has always been that way or whether the bug was introduced when the newconfigmodule was set up.Quick fix: use
bode(..., Hz=False).Proper fix: we should change the default settings to match MATLAB.
paulvicioso commentedon Feb 18, 2020
Thank you, that solved the problem.
I did not check that the frequencies were in Hz, I just made the assumption that everything was the same as in MATLAB.
[-]Bode Function produces wrong angular frequencies[/-][+]SOLVED: Bode Function produces wrong angular frequencies[/+][-]SOLVED: Bode Function produces wrong angular frequencies[/-][+]Bode plots use Hz instead of rad/sec in MATLAB compatibility mode[/+]