Absolute value of a transfer function in the frequency domain: how to calculate it.

I'd like to plot the Bode magnitude diagram of a function in the frequency domain (or better in the pulsation domain) but I'm not able to built this function that's express by the absolute values of other transfer functions .

To explain better the problem:

I have 2 transfer functions called P1(s)and P2(s) and declarated by the classical command 'tf'. Now I want to plot the Bode diagram of C that's is defined by the formula:

C(s)=(|P1|)/(1-|P2|), where the tranfer functions P1 and P2 are included in absolute value. Could anyone help me please? Thank you very much.

Answer 1

[Arkadiy Turevskiy]

Just one word of caution: the resulting C(s) will obviously be a real number, so the phase will be 0 or 180 deg depending on the sign. If that's what you want, you could do something like this:

s=tf('s');
P1=1/(s+1);
P2=5/(s^2+s+1);
[m1,p1,w1]=bode(P1);
[m2,p2]=bode(P2,w1);
C=squeeze(m1./(1-m2));
sys=frd(C,w1);
bode(sys)