How can i write a program; to find ultimate frequency of the transfer function

How can i write a program;

to find ultimate frequency of the transfer function.

i.e., frequency where the phase plot of frequency response across -pi

Answer 1

[Paul]

I guess you want the crossover frequency:

[Gm,Pm,Wgm,Wpm] = margin(sys)

Wgm is the crossover frequency in rad/s. sys is the transfer function defined by tf().