code: def data_cosine(N=1024, A=0.1, sampling=1024., freq=200):
      r
      t = arange(0, float(N)/sampling, 1./sampling)
      x = cos(2.*pi*t*freq) + A * randn(t.size)
      return x
docs: r"""Return a noisy cosine at a given frequency.
  
      :param N:           the final data size
      :param A:           the strength of the noise
      :param float sampling: sampling frequency of the input :attr:`data`.
      :param float freq:  the frequency :math:`f_0` of the cosine.
  
      .. math:: x[t] = cos(2\pi t * f_0) + A w[t]
  
      where w[t] is a white noise of variance 1.
  
      .. doctest::
  
          >>> from spectrum import data_cosine
          >>> a = data_cosine(N=1024, sampling=1024, A=0.5, freq=100)