“…To apply the integration factor technique to the compact discretization form (10), we multiply (10) by exponential matrix e −At from the left, and e −Bt from the right to obtain (11) Integration of (11) over one time step from t n to t n+1 ≡ t n + Δt, where Δt is the time step, leads to (12) To construct a scheme of rth order truncation error, we approximate the integrand in (12), (13) using a (r − 1)th order Lagrange polynomial at a set of interpolation points t n+1 , t n ,…, t n+2−r : (14) where (15) The specific form of the polynomial (15) at low orders is listed in Table 1. In terms of (τ), (12) takes the form, (16) So the new r-th order implicit schemes are (17) where α 1 , α 0 , α −1 ,···, α −r+2 are coefficients calculated from the integrals of the polynomial in (τ), (18) In Table 2, the value of coefficients, α −j , for schemes of order up to four are listed.…”