code: def calc_std_mod_reduc(mod_reduc):
          
          mod_reduc = np.asarray(mod_reduc).astype(float)
          std = (np.exp(-4.23) + np.sqrt(0.25 / np.exp(3.62) - (mod_reduc - 0.5)
                                         ** 2 / np.exp(3.62)))
          return std
docs: Calculate the standard deviation as a function of G/G_max.
  
          Equation 7.29 from Darendeli (2001).
  
          Parameters
          ----------
          mod_reduc : array_like
              Modulus reduction values.
  
          Returns
          -------
          std : :class:`numpy.ndarray`
              Standard deviation.