def _compute_mean(self, C, mag, rhypo, hypo_depth, mean, idx):
        """
        Compute mean value according to equations 10 and 11 page 226.
        """
        mean[idx] = (C['C1'] + C['C2'] * mag + C['C3'] * np.log(rhypo[idx] +
                     C['C4'] * np.exp(C['C5'] * mag)) + C['C6'] * hypo_depth)
Compute mean value according to equations 10 and 11 page 226.