For x ≥ x L = 6 this approximation is almost exact. In this case we use the Faddeeva package to evaluate the error and Dawson functions. For x < x L , the interval [0, x L ] is divided into segments at N points x 0 = 0 < x 1 < x 2 < . . . < x N-1 < x L . The initial values needed for starting the iteration according to Eqn. (60) are precalculated and hard-coded as two arrays (see table 2 below):