 This is a binary search on the cumulative array, thus reducing the worst-case time complexity of reaction sampling to O (log M).Published in 2009, 2010, and 2011 (Ramaswamy 2009, 2010, 2011).Use factored-out, partial reaction propensities to reduce the computational cost to scale with the number of species in the network, rather than the (larger) number of reactions.