Figure 2 

Convergence of selected dual-space algorithms on a two-dimensional example. (a) Two convex constraint sets with intersection. (b) Two non-convex constraint sets with several intersections. (c) Two non-convex constraint sets without intersection (unfeasible problem). All iterations start from the same point in the right-hand part of the plots. Symbols represent the actual iterates, the dotted lines connect consecutive iterates. ER = error-reduction algorithm (13), CFA = charge flipping algorithm (14), AAR = averaged alternating reflections (21), RAAR = relaxed averaged alternating reflections (24), DM = difference map [(20), with γ_M = β⁻¹, γ_D = −β⁻¹].