from sympy import symbols
from spb import *
a, s, xi = symbols("a, s, xi")
G = (s**2 + a) / (s**3 + 2*s**2 + 3*s + 4)
params={a: (-0.5, -4, 4), xi: (0.8, 0, 1)}
graphics(
    sgrid(xi, wn=False, params=params, rendering_kw={"color": "r"}),
    root_locus(G, params=params),
    grid=False, xlim=(-4, 1), ylim=(-2.5, 2.5),
    xlabel="Real", ylabel="Imaginary")