MATLAB: Bode() magnitude

bodefreqmagphase

Hi, I Have seen the code [ mag,phase] = bode(sy s) but when i try to see the values of mag, or phase, it returns something like mag(:,:,1). What is the significance of the stuff in the brackets? How can i just get the magnitude values with respect to frequency so I can plot a 2d plot of the magnitude and frequency?

thanks

Best Answer

Magnitude and phase outputs of bode are 3-D arrays, for representing multi-input multi-output systems. The first two dimensions correspond to the number of inputs and outputs, the third dimension corresponds to the number of frequency points. In your case you have a single-input single-output system, so size(mag) is 1 1 n, where n is the number of frequency points.

To get a standard bode plot you can just do

bode(sys)

If you want access to mag and phase as regular vectors, just do

mag=squeeze(mag)

All of this is covered in the doc.

Arkadiy

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MATLAB: Change marker width in bode plot

The bode function doesn’t accept many options with respect to its plots. The easiest way to do what you want is to request at least the first three outputs of the bode function, and then plot them using subplot and plot. The plots are the same as any other plot object:

[mag,phase,wout] = bode(sys);
subplot(2,1,1)
plot(wout, mag)
subplot*2,1,2)
plot(wout, phase)

Use ‘20*log10(mag)’ to plot the magnitude in decibels, and semilogx instead of plot to make the plot look like those bode produces on its own:

[mag,phase,wout] = bode(sys);
subplot(2,1,1)
semilogx(wout, 20*log10(mag))
subplot*2,1,2)
semilogx(wout, phase)

MATLAB: How to find out the TimeUnits

get(sys,'TimeUnit')

sys.TimeUnit

Best Answer

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