For example, consider the (linear) chemical system involving two chemical species X 1 and X 2 and the reaction X 1 → → X 2 . In this system, N = 2 (species), R = 1 (reactions). A state of the system is a vector X = { n 1 , n 2 } , where n 1 , n 2 are the number of molecules of X 1 and X 2 respectively. Let f 1 ( x , Ω Ω ) = n 1 Ω Ω = x 1 , so that the rate of reaction 1 (the only reaction) depends on the concentration of X 1 . The stoichiometry matrix is ( − − 1 , 1 ) T .