Reading the Stochastic Modelling of Biological Processes Lecture Notes on modelling diffusion as a chain of chemical reactions (in Section 10.2, page 45), I'm struggling to flesh out the details left to the reader of multiplying the chemical master equation by $n_i$ and summing over all possible $n$ to establish a system of ODEs for the mean equations.
My issue seems to be that because the sum is over $R^K$, I always get every term cancelling, and can't find terms that survive. Any help understanding would be greatly appreciated!
