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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_ln_sf(self, C, C_SITE, idx, n_sites, rup):
 """ Returns the log SF term required for equation 12 """

        ln_sf = np.zeros(n_sites)
        for i in range(1, 5):
            ln_sf_i = (C["lnSC1AM"] - C_SITE["LnAmax1D{:g}".format(i)])
            if i > 1:
                ln_sf_i += C["S{:g}".format(i)]
            ln_sf[idx[i]] += ln_sf_i
        return ln_sf