GILLESPIE ALGORITHM — STOCHASTIC CHEMICAL KINETICS

Exact SSA · A → B → C · Stochastic vs Deterministic Comparison

REACTION RATES

CURRENT STATE

Time t: 0.000
N_A: 100
N_B: 0
N_C: 0
Total: 100
Rxn count: 0

WAITING TIMES

Exponential waiting time dist.
Gillespie SSA (1976): exact simulation of stochastic chemical kinetics. Draw τ=-ln(U)/a₀, choose reaction by propensity. Rigorously exact — no approximation, unlike Euler-Maruyama or tau-leaping.
Top: trajectories (blue=A, green=B, pink=C, dashed=ODE)   Bottom: A-B phase plane