Stability regions in the parameter space Ei-θx. Parameters are: θy = 5. Blue shades indicate regions of bistability, red shades indicate regions of tristability. Region I corresponds to monostability, with the presence of only one stable state. Region II corresponds to bistability between two stable states. Region III corresponds to bistability between one stable state and one modulationally unstable state. Region IV corresponds to tristability between three stable states. Region V corresponds to tristability between two stable states and one modulationally unstable state. Finally, region VI corresponds to tristability between one stable state and two modulationally unstable states. Examples of two consecutive bistable curves and of a tristable curve along the dashed lines (a) and (b) are shown in Fig. 3(a) and Fig. 3(b) respectively.