FIG. 1.

Shown is that LNA gives approximate noise whereas our method gives exact noise. (a) The noise strength in two-species system (17) with $R_2^{+}(n_1,n_2)={\lambda }_2{n}_1(n_1-1)$ is taken as a function of the parameter λ₁. The other parameters are λ₂ = 10, τ₁ = 2, τ₂ = 1. (b) The noise strength in the two-species system (17) with $R_2^{+}(n_1,n_2)={\lambda }_2{n}_1(n_1-1)$ is taken as a function of the parameter λ₂. The other parameters are λ₁ = 1, τ₁ = 2, τ₂ = 1.