(color online) State variables synchronization for the four drive systems (21)–(25) (solid curves) and the four response system (26)–(29) (dashed curves): (a) (x11 + 2x21)(x31 + 5x41) and (2y11 + 4y21 + y31 + 2y41) versus t; (b) (−x12 + 2x22)(x32 + x42) and (3y12 + y22 − y32 + 3y42) versus t; (c) (2x13 + 2x23) (−x33 − x43) and (2y13 + 3y23 + 2y33 − y43) versus t; (d) (x14 + 2x24)(2x34 + x44) and (2y14 − 2y24 + 3y34 + y44) versus t.
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