All one-step methods can be expressed in this general form, with the only difference
being the manner in which the slope is estimated. As in the falling parachutist problem, the
simplest approach is to use the differential equation to estimate the slope in the form of the
first derivative at xi. In other words, the slope at the beginning of the interval is taken as an
approximation of the average slope over the whole interval. This approach, called Euler’s
method, is discussed in the first part of this chapter. This is followed by other one-step
methods that employ alternative slope estimates that result in more accurate predictions.
All these techniques are generally called Runge-Kutta methods.