Legend does not recognize semilogx plot

The legend I plot does not recognize all my plots. I have 1 bode plot (only the magnitude) and 2 semilogx plots. The first two semilogx plots do not seem to appear in the legend. Logically, Matlab also tells me that it is ignoring 'extra' legend entries.

This is my relevant code

figure(5),clf(5)

p = bodeoptions('cstprefs');

p.FreqUnits = 'rad/s';

p.PhaseVisible = 'off';

hold on

semilogx(w,spec_y(1:length(f)),'r')

semilogx(w,spec_y0(1:length(f)),'b')

bodeplot(G0,p,'g');

legend('y','y0','Exact')

grid on

%set(gca, 'XScale', 'log');

xlabel('w (rad/s)')

ylabel('|Mag| (dB)')

This is the output, showing only the first legend entry for the 'bodeplot(G0,p,'g')' plot.

Answer 1

[Star Strider]

I have no idea what the other values are that you are plotting on the bodeplot axes. Apparently, the only legend entries bodeplot permits are the systems it plots.

It might be easier to get the data from bodeplot and plot everything on ‘ordinary’ axes.

This outlines how to get those data from bodeplot —

sys = tf([1 0 0],[1 1 1 1 1])

sys =
 
            s^2
  -----------------------
  s^4 + s^3 + s^2 + s + 1
 
Continuous-time transfer function.

h = bodeplot(sys)

h =

	resppack.bodeplot

Frq = h.Responses.Data.Frequency

Frq = 72×1

0.0000 0.0000 0.0000 0.0000 0.0000 0.0020 0.0200 0.0234 0.0273 0.0320

Mag = h.Responses.Data.Magnitude

Mag = 72×1

0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0004 0.0005 0.0007 0.0010

Phs = h.Responses.Data.Phase

Phs = 72×1

-3.1416 -3.1416 -3.1416 -3.1416 -3.1416 -3.1436 -3.1616 -3.1650 -3.1689 -3.1736

.