code: def calc_std_damping(damping):
          
          damping = np.asarray(damping).astype(float)
          std = (np.exp(-5) + np.exp(-0.25) * np.sqrt(100 * damping)) / 100.
          return std
docs: Calculate the standard deviation as a function of damping in decimal.
  
          Equation 7.30 from Darendeli (2001).
  
          Parameters
          ----------
          damping : array_like
              Material damping values in decimal.
  
          Returns
          -------
          std : :class:`numpy.ndarray`
              Standard deviation.