Bayesian information criterion (BIC) evaluated for the data from Figure 5 and different kernel choices. The x-axis shows the number of terms included in each model. The blue circles show models where the terms have been summed, and the orange squares indicate that the model is a product of terms. In the product models, the parameters S₀ and Q are held fixed at 1 and ﹩1/\sqrt{2}﹩, respectively, for all but the first term. The dashed black line shows the minimum value of the BIC, and this corresponds to the model chosen in the text.