code: def make_frequency_series(vec):
      
      if isinstance(vec, FrequencySeries):
          return vec
      if isinstance(vec, TimeSeries):
          N = len(vec)
          n = N/2+1
          delta_f = 1.0 / N / vec.delta_t
          vectilde =  FrequencySeries(zeros(n, dtype=complex_same_precision_as(vec)),
                                      delta_f=delta_f, copy=False)
          fft(vec, vectilde)
          return vectilde
      else:
          raise TypeError("Can only convert a TimeSeries to a FrequencySeries")
docs: Return a frequency series of the input vector.
  
      If the input is a frequency series it is returned, else if the input
      vector is a real time series it is fourier transformed and returned as a
      frequency series.
  
      Parameters
      ----------
      vector : TimeSeries or FrequencySeries
  
      Returns
      -------
      Frequency Series: FrequencySeries
          A frequency domain version of the input vector.