(Color online) The “clumping” instability of traveling waves and the formation of finite pulse trains at av = 0.6 in small periodic domains with period (a) L = 2λc ≃ 8.14, (b) L = 3λc ≃ 12.21, and (c) L = 4λc ≃ 16.28. The background state filling the domain corresponds to the homogeneous state U0 ≡ (u0, v0, w0) ≃ (−0.650, −0.375, −0.650). Left panels: space-time plots with x along the vertical axis and time horizontally (dark colour indicates larger values of the u field). Right panels: profiles of finite pulse trains at t = 390, traveling without change towards the right.