docs: def _position_autocorrelation_fitting_eqn(t, Gamma, AngTrapFreq):
      """
      The value of the fitting equation:
      exp(-t*Gamma/2) * (cos(t* sqrt(Omega**2 - Gamma**2 /4)) + Gamma* sin(t* sqrt(Omega**2-Gamma**2 /4))/(2* sqrt(Omega**2 - Gamma**2 /4)))
      [eqn 4.20 taken from DOI: DOI: 10.1007/978-1-4614-6031-2]
      to be fit to the autocorrelation-exponential decay
  
      Parameters
      ----------
      t : float
          time 
      Gamma : float
          Big Gamma (in radians), i.e. damping 
      AngTrapFreq : float
          Angular Trapping Frequency in Radians
  
      Returns
      -------
      Value : float
          The value of the fitting equation
      """
      return _np.exp(-t*Gamma/2)* ( _np.cos(t* _np.sqrt(AngTrapFreq**2-Gamma**2/4)) + Gamma* _np.sin(t* _np.sqrt(AngTrapFreq**2-Gamma**2/4))/(2* _np.sqrt(AngTrapFreq**2-Gamma**2/4)) )