2.4.2 Example: Quadratic Interpolation
Suppose we want to interpolate a quadratic polynomial between the five points (x[k], y[k]) of Exhibit 2.5.
The general form for a quadratic polynomial from 2 to is
Solving for the six constants βj based upon the five points (x[k], y[k]) of Exhibit 2.5 would entail a system of five equations in six unknowns. Such a system is likely to have infinitely many solutions. To obtain a unique solution, we may consider a less general form of quadratic polynomial than [2.40]. We might require β5 = β4 or set β1 = 0, etc. For this example, let’s interpolate a quadratic polynomial with zero cross term, β6 = 0. Our polynomial then has form
We require that this polynomial intercept each of our five points. This renders a system of five equations in five unknowns, which we express in matrix notation as
Solving, we obtain
This and the five points are graphed in Exhibit 2.6.