(color online) (a) Variations of radial Gini coefficient, , with propelling force. The inset shows the schematic diagram of partitioning the space radially (left) and angularly along the boundary (right) for calculating the radial and angular Gini coefficients, respectively. (b) Variations of angular Gini coefficient, , with propelling force. The inset shows the magnified parts of curves at small forces. (The standard deviations of the data in panels (a) and (b) are less than 0.09 and the standard errors of the mean are less than .)