(color online) Chaotic attractor of system (21) when c11 = 15.6, c12 = 3, c13 = 21, c14 = 15, c15 = 0.5 and x10 = diag (0.2, 0.2, 0.2, 0.2): (a) x14, x11, x13 space, (b) x11, x12 space, (c) x13, x14 space, (d) x12, x14 space.