Coagulation: Smoluchowski Equation

The Smoluchowski coagulation equation ∂n_k/∂t = ½Σ K(i,j)n_i·n_j [i+j=k] − n_k Σ K(k,j)n_j describes cluster growth. Constant kernel K=const gives exponential decay; product kernel K∝ij exhibits gelation — a phase transition at finite time.