erpretation:

        * 1 (instance of `lti`)
        * 2 (num, den)
        * 3 (zeros, poles, gain)
        * 4 (A, B, C, D)

w : array_like, optional
    Array of frequencies (in rad/s). Magnitude and phase data is calculated
    for every value in this array. If not given a reasonable set will be
    calculated.
n : int, optional
    Number of frequency points to compute if `w` is not given. The `n`
    frequencies are logarithmically spaced in an interval chosen to
    include the influence of the poles and zeros of the system.

Returns
-------
w : 1D ndarray
    Frequency array [rad/s]
mag : 1D ndarray
    Magnitude array [dB]
phase : 1D ndarray
    Phase array [deg]

Notes
-----
If (num, den) is passed in for ``system``, coefficients for both the
numerator and denominator should be specified in descending exponent
order (e.g. ``s^2 + 3s + 5`` would be represented as ``[1, 3, 5]``).

.. versionadded:: 0.11.0

Examples
--------
>>> from scipy import signal
>>> import matplotlib.pyplot as plt

>>> sys = signal.TransferFunction([1], [1, 1])
>>> w, mag, phase = signal.bode(sys)

>>> plt.figure()
>>> plt.semilogx(w, mag)    # Bode magnitude plot
>>> plt.figure()
>>> plt.semilogx(w, phase)  # Bode phase plot
>>> plt.show()

r‡