# scipy.signal.freqs_zpk

scipy.signal.freqs_zpk(z, p, k, worN=200)

  Compute frequency response of analog filter.

  Given the zeros z, poles p, and gain k of a filter, compute its frequency response:

                 (jw-z[0]) * (jw-z[1]) * ... * (jw-z[-1])
      H(w) = k * ----------------------------------------
                 (jw-p[0]) * (jw-p[1]) * ... * (jw-p[-1])

  Parameters:
    z array_like

      Zeroes of a linear filter

    p array_like

      Poles of a linear filter

    k scalar

      Gain of a linear filter

    worN{None, int, array_like}, optional

      If None, then compute at 200 frequencies around the interesting parts of the response curve (determined by pole-zero locations). If a single integer, then compute at that many frequencies. Otherwise, compute the response at the angular frequencies (e.g., rad/s) given in worN.

  Returns:
    w ndarray

      The angular frequencies at which h was computed.

    h ndarray

      The frequency response.

  See also

  `freqs`

    Compute the frequency response of an analog filter in TF form

  `freqz`

    Compute the frequency response of a digital filter in TF form

  `freqz_zpk`

    Compute the frequency response of a digital filter in ZPK form

  Notes

  New in version 0.19.0.

  Examples

      >>> import numpy as np
      >>> from scipy.signal import freqs_zpk, iirfilter

      >>> z, p, k = iirfilter(4, [1, 10], 1, 60, analog=True, ftype='cheby1',
      ...                     output='zpk')

      >>> w, h = freqs_zpk(z, p, k, worN=np.logspace(-1, 2, 1000))

      >>> import matplotlib.pyplot as plt
      >>> plt.semilogx(w, 20 * np.log10(abs(h)))
      >>> plt.xlabel('Frequency')
      >>> plt.ylabel('Amplitude response [dB]')
      >>> plt.grid(True)
      >>> plt.show()