since the relation in (12.18) maps −1 to a, the midpoint 0 to (a + b)/2, and the
right endpoint b to 1. If we insert this in (12.19), we obtain Simpson’s rule for
the general interval [a,b], see figure 12.5a. In practice, we will usually divide the
interval [a,b] into smaller ntervals and use Simpson’s rule on each subinterval,
see figure 12.5b.