Figure 1. The RFM models unidirectional flow along a chain of n sites.

The state variable represents the density at site i at time t. The parameter λ_i > 0 controls the transition rate from site i to site i + 1, with λ₀ > 0 [λ_n > 0] controlling the initiation [exit] rate. The output rate at time t is R(t) = λ_nx_n(t).