from sympy.abc import a, b, c, s
from spb import *
from sympy.physics.control.lti import TransferFunction
tf = TransferFunction(a*s**2 + b*s + c, s**3 + 10*s**2 + 5 * s + 1, s)
params = {
    a: (-25, -100, 100),
    b: (60, -300, 300),
    c: (-100, -1000, 1000),
}
graphics(
    nichols(tf, omega_limits=[1e-03, 1e03], n=1e04, params=params),
    xlabel="Open-Loop Phase [deg]",
    ylabel="Open-Loop Magnitude [dB]",
    xlim=(-360, 360), grid=False,
)