This forward difference is but one of many that can be developed from the Taylor series to approximate
derivatives numerically. For example, backward and centered difference approximations of the first derivative can
be developed in a fashion similar to the derivation of Eq. (4.19). The former utilizes values at xi - 1 and xi (Fig.
4.10b), whereas the latter uses values that are equally spaced around the point at which the derivative is estimated
(Fig. 4.10c). More accurate approximations of the first derivative can be developed by including higher-order
terms of the Taylor series. Finally, all the foregoing versions can also be developed for second, third, and higher
derivatives. The following sections provide brief summaries illustrating how some of these cases are derived.