p_margin - phase margin
The phase margin is the values of the phase at points where the nyquist plot of h crosses the unit circle.
h=syslin('c',-1+%s,3+2*%s+%s^2)
[p,fr]=p_margin(h)
[p,fr]=p_margin(h+0.7)
nyquist(h+0.7)
t=(0:0.1:2*%pi)';plot2d(sin(t),cos(t),-3,'000')