from sympy.abc import a, b, c, s
from spb import plot_nichols
from sympy.physics.control.lti import TransferFunction
tf = TransferFunction(a*s**2 + b*s + c, s**3 + 10*s**2 + 5 * s + 1, s)
plot_nichols(
    tf, omega_limits=[1e-03, 1e03], n=1e04,
    params={
        a: (-25, -100, 100),
        b: (60, -300, 300),
        c: (-100, -1000, 1000),
    },
    xlim=(-360, 360)
)