code: def window_poisson(N, alpha=2):
      r
      n = linspace(-N/2., (N)/2., N)
      w = exp(-alpha * abs(n)/(N/2.))
      return w
docs: r"""Poisson tapering window
  
      :param int N: window length
  
      .. math:: w(n) = \exp^{-\alpha \frac{|n|}{N/2} }
  
      with :math:`-N/2 \leq n \leq N/2`.
  
      .. plot::
          :width: 80%
          :include-source:
  
          from spectrum import window_visu
          window_visu(64, 'poisson')
          window_visu(64, 'poisson', alpha=3)
          window_visu(64, 'poisson', alpha=4)
  
      .. seealso:: :func:`create_window`, :class:`Window`