How to change the default x-axis unit in a Bode diagram to Hertz?

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Rad/s is nice for mechanical people, but I'm an EE, and I much prefer Hertz. It should be something simple, but I can't find it in the help.
  2 Comments
dpb
dpb on 22 Sep 2018
Don't believe there is a way in the base routine; it's built entirely around rad/timeunits per the system object.
You could write a wrapper routine to convert frequency units and update the plot labels.
Chris
Chris on 4 Jan 2025
Actually you can, click on the plot tab from linearization manager, click plot properties, click units. Change to whatever units you need.

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Accepted Answer

Star Strider
Star Strider on 22 Sep 2018
Use bodeplot (link) instead of bode.
It gives you that option, and the documentation specifically mentions that.
  4 Comments
marcel hendrix
marcel hendrix on 22 Sep 2018
I've put the below function in my userpath . It'll do for now.
% a new bode() command that has Hz as default
function h = bodef(x)
P = bodeoptions; P.FreqUnits = 'Hz';
h = bodeplot(x,P);
Star Strider
Star Strider on 22 Sep 2018
Edited: Star Strider on 22 Sep 2018
That is what I would do.
I defer to bodeplot because it allows some customization. I use and plot the bode outputs only if I want other options.
EDIT
I add that this was my original recommendation!

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More Answers (3)

Tjeerd Ickenroth
Tjeerd Ickenroth on 31 May 2023
Type 'ltiview' in your command window. The Linear System Analyzer will pop up. Click on: File --> Toolbox Preferences... --> Units --> Frequency: Hz
  3 Comments
Tjeerd Ickenroth
Tjeerd Ickenroth on 31 May 2023
You need to change it once in the GUI and you always obtain bode plots in Hz. The setting remains even when you restart Matlab.
marcel hendrix
marcel hendrix on 31 May 2023
And what when I share my function/script with others? Or use different (older) versions of MATLAB?

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Dimitris Kalogiros
Dimitris Kalogiros on 22 Sep 2018
clc;close all; clc
% test system
s=tf('s');
H=(s-1)/((s-3)*(s-2))
% bode
[mag,phase,wout] = bode(H);
%plot results, with frequency expressed at Hz
figure;
subplot(2,1,1);
semilogx(wout(:,1)/(2*pi), 20*log10(squeeze(mag)), '-b'); zoom on; grid on;
title('magnitude'); xlabel('Frequency (Hz)'); ylabel('Magnitude (dB)');
subplot(2,1,2);
semilogx(wout(:,1)/(2*pi), squeeze(phase), '-r'); zoom on; grid on;
title('Phase'); xlabel('Frequecy (Hz)'); ylabel('Phase (deg)');
  2 Comments
Charl
Charl on 15 Mar 2024
Edited: Charl on 15 Mar 2024
This is the correct answer. Some of the others simply change the label to Hz without rescaling.
Meth Hai
Meth Hai on 15 Jul 2024
%%% G1 & and G2 is your TFs
[mag1, phase1, wout1] = bode(G1);
[mag2, phase2, wout2] = bode(G2);
% Convert angular frequency (rad/s) to frequency (Hz)
freq1 = wout1 / (2 * pi);
freq2 = wout2 / (2 * pi);
% Plot the magnitude response
figure;
subplot(2,1,1);
semilogx(freq1, 20*log10(squeeze(mag1)), '-b');
hold on;
semilogx(freq2, 20*log10(squeeze(mag2)), '-g');
grid on;
title('Magnitude');
xlabel('Frequency (Hz)');
ylabel('Magnitude (dB)');
legend('G1', 'G2');
%%%%%%%%%%%%
% Plot the phase response
subplot(2,1,2);
semilogx(freq1, squeeze(phase1), '-r');
hold on;
semilogx(freq2, squeeze(phase2), '-m');
grid on;
title('Phase');
xlabel('Frequency (Hz)');
ylabel('Phase (deg)');
legend('G1', 'G2');

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Paul
Paul on 5 Jan 2025
ctrlpref allows one to change the default units for frequency axis when plotting with bode and bodeplot (among other defaults in the Control System Toolbox). As far as I know, this preference only affects the plot, it doesn't affect the the third output from bode if using output arguments.
  4 Comments
marcel hendrix
marcel hendrix on 5 Jan 2025
This is fine, but I wanted thet getter/setters to make sure that my programs work as intended when I share the file with somebody else, or when I work on a different machine in a different location under a different account. I am not a fan of storing everything in the cloud on potentially hostile servers, so I'd like to store these things explicitly in the code. The features I mentioned would help help in (re)setting the environment, which is always a huge hassle.
Paul
Paul on 6 Jan 2025
Some things can be controlled programatically via settings. See Access and Modify Settings. Unfortunately, these don't cover the Control System Toolbox (why not?). As far as I know, the only way to deal with the CST is via ctrlpref, for which there is no programmatic interface (why not?), as far as I know. Those CST preferences are saved to disk somewhere somehow, so it might be possible copy them from one machine to another. You may want to open up a new question on this topic.
s = settings
s =
SettingsGroup with properties: drivingscenario: [1x1 SettingsGroup] matlab: [1x1 SettingsGroup] kits_common: [1x1 SettingsGroup] Simulink: [1x1 SettingsGroup] database: [1x1 SettingsGroup] roadrunner: [1x1 SettingsGroup] driving: [1x1 SettingsGroup] comparisons: [1x1 SettingsGroup] parallel: [1x1 SettingsGroup]

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