The time evolution of Π Π is then governed by the linear Fokker–Planck equation with coefficient matrices A and B B T (in the large- Ω Ω limit, terms of O ( Ω Ω − − 1 / 2 ) may be neglected, termed the linear noise approximation). With knowledge of the reaction rates f and stoichiometry S , the moments of Π Π can then be calculated.