where, yi(t)∈ R, are the states of

where, yi(t)∈ R, are the states of slave system and y(t)=[y1(t), y2(t), · · ·, yn(t)]Tis the state vector. gi(y), i =1, · · ·, n is known smooth functions. gi(y) represents the system uncertainties. di(t)are unknown bounded external dis-turbance. biis the unknown control gain. vi(t)is the synchronization controller output to be designed, u(vi(t))denotes thecontrol input subject to saturation type nonlinearity. The control direction is unknown, i.e., the sign of biis unknown as well.