Potential and forces for the Ferrers bar with different redistribution numbers of particles. In each panel, the black line is the results for the model given by the analytical method. The red, blue and green lines represent the result in the CylSP method with R_min = 0.1, R_min = 0.01 and the value provided by AGAMA, respectively. From left to right: the results for N-body realizations with particle number 2 × 10⁵, 5 × 10⁵, 10⁶, and 10⁷, respectively.