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Module « scipy.signal »

Fonction dfreqresp - module scipy.signal

Signature de la fonction dfreqresp

def dfreqresp(system, w=None, n=10000, whole=False) 

Description

help(scipy.signal.dfreqresp)

Calculate the frequency response of a discrete-time system.

Parameters
----------
system : an instance of the `dlti` class or a tuple describing the system.
    The following gives the number of elements in the tuple and
    the interpretation:

        * 1 (instance of `dlti`)
        * 2 (numerator, denominator, dt)
        * 3 (zeros, poles, gain, dt)
        * 4 (A, B, C, D, dt)

w : array_like, optional
    Array of frequencies (in radians/sample). 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.
whole : bool, optional
    Normally, if 'w' is not given, frequencies are computed from 0 to the
    Nyquist frequency, pi radians/sample (upper-half of unit-circle). If
    `whole` is True, compute frequencies from 0 to 2*pi radians/sample.

Returns
-------
w : 1D ndarray
    Frequency array [radians/sample]
H : 1D ndarray
    Array of complex magnitude values

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. ``z^2 + 3z + 5`` would be represented as ``[1, 3, 5]``).

.. versionadded:: 0.18.0

Examples
--------
Generating the Nyquist plot of a transfer function

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

Construct the transfer function
:math:`H(z) = \frac{1}{z^2 + 2z + 3}` with a sampling time of 0.05
seconds:

>>> sys = signal.TransferFunction([1], [1, 2, 3], dt=0.05)

>>> w, H = signal.dfreqresp(sys)

>>> plt.figure()
>>> plt.plot(H.real, H.imag, "b")
>>> plt.plot(H.real, -H.imag, "r")
>>> plt.show()

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