“…To simulate the bracket motion of the nilpotent approximation, we choose the initial state q 0 and apply the periodic input on couples (N 1 , N 2 ), (N 1 , N 3 ) and (N 1 , N 4 ) to receive the displacement approximately parallel to [N 1 , N 2 ], [N 1 , N 3 ] and [N 1 , N 4 ] respectively [19]. More precisely, for one cycle we apply u 1 (t) = −Aω sin(ωt), u i (t) = Aω cos(ωt), u j (t) = 0, u k (t) = 0 for i ∈ {2, 3, 4} and j, k ∈ {2, 3, 4} − {i}, respectively, all with respect to the control system (10), amplitude A = 0.4 and angular speed ω = 2π 50 . Then we apply the same process to original vector fields X 1 , X 2 , X 3 and X 4 .…”