Gain/phase margin calculation and the gain/phase cross over frequency

Hello..

I used the below code to calculate the gain and phase margin. Also to calculate gain and phase cross over frequency but I didn't get any answer in the command window. So, what is the correct code.

syms s
G = tf([7 14],[1 10 24])
[Gm,Pm,Wcg,Wcp] = margin(G)
grid on

Answer 1

[Alexandre Riebel]

I'd say your code is working correctly. Phase margin is measured at the frequency at which the gain crosses the 0 dB line (gain crossover frequency, Wcg) and gain margin is measured at the frequency at which the phase crosses the -180 deg line (phase crossover frequency, Wcp). So if your gain never crosses 0 dB then wcg = NaN and Pm = Inf which seems to be what's happening here.

[Mahabba Almheiri]

thank you.. I have one more question..

Then what about the Gm and Wcp. If the result in command window is like that below

Gm =

Inf

Pm =

Inf

Wcg =

NaN

Wcp =

NaN