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.

def calc_std_damping(damping):
        """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.
        """
        damping = np.asarray(damping).astype(float)
        std = (np.exp(-5) + np.exp(-0.25) * np.sqrt(100 * damping)) / 100.
        return std