Procedure for obtaining a functional form for the attenuation curve, A_λ/A_V, as a function of wavelength, λ, and the IOB latent variables, {I_i}, with symbolic regression. We find that more interpretable results are obtained if we first fit a function to the broadband features of the curve, f(x, {I_i}), by masking the wavelength range containing the bump (gray band in second plot). An analytic expression for the residuals of this function is then found, g(x, {I_i}), before the terms are summed and any free parameters are re-optimized.