code: def _get_ln_sf(self, C, C_SITE, idx, n_sites, rup):
          
          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
docs: Returns the log SF term required for equation 12