The last expression can be rewritten in matrix form ∆σ = (∆σ 1 , ..., ∆σ Nc ) T = Aζ Because the α k i coefficients remain the same, matrix A is computed once at the start of the simulation. At each step, the elements ∆σ k are evaluated as the difference between the σ k (λ u ) and σ k (λ c ) = C k :