def _compute_mean(self, C, f0, f1, f2, SC, mag, rrup, idxs, mean,
                      scale_fac):
        """
        Compute mean value (for a set of indexes) without site amplification
        terms. This is equation (5), p. 2191, without S term.
        """
        mean[idxs] = (C['c1'] +
                      C['c2'] * mag +
                      C['c3'] * (mag ** 2) +
                      (C['c4'] + C['c5'] * mag) * f1[idxs] +
                      (C['c6'] + C['c7'] * mag) * f2[idxs] +
                      (C['c8'] + C['c9'] * mag) * f0[idxs] +
                      C['c10'] * rrup[idxs] +
                      self._compute_stress_drop_adjustment(SC, mag, scale_fac))
Compute mean value (for a set of indexes) without site amplification
        terms. This is equation (5), p. 2191, without S term.