The charge flipping algorithm

Oszlányi, G.; Sütő, A.

doi:10.1107/S0108767307046028

Figure 7
The real space of the two-pixel charge flipping algorithm. The non-convex manifold of fixed points is the union of two half-infinite lines and a quarter-plane. Blue and red arrows correspond to an example of the CF transformation, $[(\rho_x,\rho_y) \rightarrow (\rho_x,-\rho_y)]$ , which increases the distance to the manifold.