code: def _compute_nonlinear_soil_term(self, C, lnSA_AB, delta_C, delta_D):
          
  
          lnSA_CD = (
              # line 1 equation 4 without first term (lnSA_AB)
              C['c29'] * delta_C +
              # line 2 and 3
              (C['c30as'] * np.log(np.exp(lnSA_AB) + 0.03) + C['c43']) * delta_D
              )
  
          return lnSA_CD
docs: Compute mean value on site class C/D (equation 4 on page 22 without
          the first term)