Here we define the weight for edge \\(e(t,x,x')\\):

* Weight(e(t,x,x')) = RateConstant(t) * \\(\prod_{\mathit{species} \in S}\\) FallingPower(Population(x,species), InpDegree(t, species))

Where:

* FallingPower(n, k) = n * (n-1) * ... * (n - k + 1)

This gives the "rate of probability flow" through the edge.