Vicsek model: θᵢ(t+1) = ⟨θⱼ⟩|rᵢⱼ|<r + η·ξᵢ
where ξᵢ∈[−π,π] is angular noise. At low noise and high density, particles spontaneously order (flock). At intermediate noise, motility-induced phase separation (MIPS) clusters dense bands of synchronized swimmers against a dilute gas.