“…k (t), where x (1) k (t), x (2) k (t) are the states without noise disturbance, d (1) k (t) and d (2) k (t) are the measurement noise of x (1) k (t) and x (2) k (t), respectively. Denote state tracking errors are e 1k (t) = x (1) d (t) À x (1) k (t) and e 2k (t) = x (2) d (t) À x (2) k (t), where x (1) d (t) and x (2) d (t) are the desired states, while actual measurement errors are e 1k (t) = x (1) d (t) À x (1) m, k (t), e 2k (t) = x (2) d (t) À x (2) m, k (t). So we can know e 1k (t) = e 1k (t) À d (1) k (t), e 2k (t) = e 2k (t) Àd (2) k (t).…”