Gillespie Algorithm
Exact stochastic simulation of chemical reactions
Reaction System
System
Birth-Death
Genetic Toggle
Michaelis-Menten
SIR Epidemic
Rate k₁
1.00
Rate k₂
0.10
Trajectories
5
Run Simulation
Clear
Time:
0
Species:
—
Trajectories:
0
complete
Gillespie (1977)
: exactly samples the chemical master equation. At each step, compute total propensity a₀=Σaᵢ, draw next event time τ~Exp(a₀), choose reaction j with prob aⱼ/a₀. Captures fluctuations invisible to ODEs — critical at low copy numbers.