The reaction rate coefficient k j is computed using Maximum Likelihood Estimation which requires several assumptions. The first assumption is that the time interval ∆t is short enough that the propensity function can be considered as constant between two timesteps. The second assumption is that the number of occurrences n j (t, t+∆t) of the reaction j between time t and t+∆t follows a Poisson distribution with parameter a j (X(t))∆t. The last assumption is that the Poisson random variables of all reactions are conditionally independent given X(t). Using these assumptions the reaction rate coefficient k j can be estimated using Maximum Likelihood Estimation: