code: def frequency_from_polarizations(h_plus, h_cross):
      
      phase = phase_from_polarizations(h_plus, h_cross)
      freq = numpy.diff(phase) / ( 2 * lal.PI * phase.delta_t )
      start_time = phase.start_time + phase.delta_t / 2
      return TimeSeries(freq.astype(real_same_precision_as(h_plus)),
          delta_t=phase.delta_t, epoch=start_time)
docs: Return gravitational wave frequency
  
      Return the gravitation-wave frequency as a function of time
      from the h_plus and h_cross polarizations of the waveform.
      It is 1 bin shorter than the input vectors and the sample times
      are advanced half a bin.
  
      Parameters
      ----------
      h_plus : TimeSeries
          A PyCBC TimeSeries vector that contains the plus polarization of the
          gravitational waveform.
      h_cross : TimeSeries
          A PyCBC TimeSeries vector that contains the cross polarization of the
          gravitational waveform.
  
      Returns
      -------
      GWFrequency : TimeSeries
          A TimeSeries containing the gravitational wave frequency as a function
          of time.
  
      Examples
      --------
      >>> from pycbc.waveform import get_td_waveform, phase_from_polarizations
      >>> hp, hc = get_td_waveform(approximant="TaylorT4", mass1=10, mass2=10,
                           f_lower=30, delta_t=1.0/4096)
      >>> freq = frequency_from_polarizations(hp, hc)