Algorithm 1.

Hybrid method.

1.	Initialize the system. Set the time t = 0. Let T be the length of the simulation.
2.	Assign molecules to the mesoscopic and microscopic subsets according to F(S, t).
3.	Simulate the mesoscopic molecules for Δt seconds. Mesoscopic molecules cannot interact with microscopic molecules during the time step. Any molecules produced will, for the remainder of the time step, be simulated on the mesoscopic scale.
4.	Simulate the microscopic molecules for Δt seconds, while freezing the mesoscopic molecules. Microscopic molecules can react mesoscopically with mesoscopic molecules. Any molecules produced will, for the remainder of the time step, be simulated on the microscopic scale.
5.	Add Δt to t.
6.	Repeat 2-5 until t = T.