from sympy.abc import s
from sympy.physics.control.lti import TransferFunction
from spb import *
tf = TransferFunction(50*s**2 - 20*s + 15, -10*s**2 + 40*s + 30, s)
graphics(
    nichols(tf),
    xlabel="Open-Loop Phase [deg]",
    ylabel="Open-Loop Magnitude [dB]",
    grid=False
)