Before revision:  By adapting a method based on  the discrete-time Markov process , we provide here a general analytic tool for the reaction dynamics of systems with a small number of molecules. Bistability induced by the small-number effect in a two-component model is analyzed and excellent agreement with the simulated mean switching time is demonstrated.
After revision:  By adapting a method based on the small-number effect in a two-component model is analyzed and excellent agreement with the simulated mean switching time is demonstrated.