(c) Deterministic mean and single SSA trajectory for p53 system. (d) Deterministic mean and 9 points taken from different SSA trajectories for p53 system. []{data-label="p53figure5"}](Figure7){width="48.00000%"}

Computational Complexity
------------------------

The computational complexity of the moment approximation method depends on the number of variables in the system, and the number of terms that need to be evaluated for each central moment. Because of the symmetry of central moments, e.g. $\left<(x_1-\mu_1)(x_2-\mu_2)\right>=\left<(x_2-\mu_2)(x_1-\mu_1)\right>$, there are many terms we do not need to include in the ODE representation of the system. The total number of central moment terms that could be nonzero when approximating a system with $d$ variables and up to $N$ moments is given by $$\begin{aligned}
N_{cm}=\frac{(N+d)!}{N!d!}-d-1\end{aligned}$$ We subtract $d$ terms because the first order central moments are always zero, and one term corresponding to the zeroth order central moment. For the deterministic case, the total number of ODE equations necessary to describe the system is equal to the number of variables, each term describes the mean of one of the variables. For the LNA the total number of equations is equal to the number of equations needed for the two moment approximation. We displayed the number of central moment terms to be evaluated 