code: def nuttall(M, sym=True):
      """Return a minimum 4-term Blackman-Harris window according to Nuttall.
  
      This variation is called "Nuttall4c" by Heinzel. [2]_
  
      Parameters
      ----------
      M : int
          Number of points in the output window. If zero or less, an empty
          array is returned.
      sym : bool, optional
          When True (default), generates a symmetric window, for use in filter
          design.
          When False, generates a periodic window, for use in spectral analysis.
  
      Returns
      -------
      w : ndarray
          The window, with the maximum value normalized to 1 (though the value 1
          does not appear if `M` is even and `sym` is True).
  
      References
      ----------
      .. [1] A. Nuttall, "Some windows with very good sidelobe behavior," IEEE
             Transactions on Acoustics, Speech, and Signal Processing, vol. 29,
             no. 1, pp. 84-91, Feb 1981. :doi:`10.1109/TASSP.1981.1163506`.
      .. [2] Heinzel G. et al., "Spectrum and spectral density estimation by the
             Discrete Fourier transform (DFT), including a comprehensive list of
             window functions and some new flat-top windows", February 15, 2002
             https://holometer.fnal.gov/GH_FFT.pdf
  
      Examples
      --------
      Plot the window and its frequency response:
  
      >>> from scipy import signal
      >>> from scipy.fftpack import fft, fftshift
      >>> import matplotlib.pyplot as plt
  
      >>> window = signal.nuttall(51)
      >>> plt.plot(window)
      >>> plt.title("Nuttall window")
      >>> plt.ylabel("Amplitude")
      >>> plt.xlabel("Sample")
  
      >>> plt.figure()
      >>> A = fft(window, 2048) / (len(window)/2.0)
      >>> freq = np.linspace(-0.5, 0.5, len(A))
      >>> response = 20 * np.log10(np.abs(fftshift(A / abs(A).max())))
      >>> plt.plot(freq, response)
      >>> plt.axis([-0.5, 0.5, -120, 0])
      >>> plt.title("Frequency response of the Nuttall window")
      >>> plt.ylabel("Normalized magnitude [dB]")
      >>> plt.xlabel("Normalized frequency [cycles per sample]")
  
      """
      return general_cosine(
          M, [0.3635819, 0.4891775, 0.1365995, 0.0106411], sym
      )
  
imports: from __future__ import division, print_function, absolute_import
  import operator
  import warnings
  import numpy
  from scipy import fftpack, linalg, special
  from scipy._lib.six import string_types
label_desc: Use image node_id 10 for calling a global function with example usage: nuttall(M, sym) and returns: general_cosine