Potential and forces for the barred galaxy models and their individual components. From left to right: the input density model is the Ferrers bar, the MN disk, the Plummer halo, and the total, i.e., bar + disk + halo, respectively. In each panel, the black line corresponds to the results for the model given by the analytical method directly. The red, blue, and green lines are the results for the HO method with (n_max, l_max) = (16,12), (12,12), and (6,4), respectively.