At initialization, the number of extremals in the pass and stop band could be assigned by using the ratio of the sizes of the bands. Furthermore, the pass and stop band edge would always be placed in the extremal set, and the program's logic kept those edge frequencies in the extremal set. The movement between bands was controlled by comparing the size of the errors at all the candidate extremal frequencies and taking the largest. The second element of the algorithm was the interpolation step needed to evaluate the error function. They used a method called the Barycentric form of Lagrange interpolation, which was very robust.