N coupled oscillators with random natural frequencies. Above critical coupling K_c = 2σ, a synchronized cluster emerges — the order parameter r jumps from 0 to positive.
dθᵢ/dt = ωᵢ + (K/N)Σⱼsin(θⱼ−θᵢ) | r·e^iψ = (1/N)Σe^iθⱼ | K_c = 2σ√(π/2)