Lagrange interpolation

Syntax: | `vout = INTERPOLATE(x,y,xout,'LAGRANGE')`

If the `LAGRANGE` keyword is used, the interpolating method used is general Lagrange interpolation. The degree of the interpolating polynomial depends on the number of input data points.

Suppose that `N` is the number of points, equal to the lengths of `x` and `y`. If `N = 2`, then a simple straight line is used for interpolating. If `N = 3` or `N = 4`, then a quadratic is used. If `N ≥ 5`, then a polynomial of degree `4` is used for the interpolation.

Spline interpolation
Fritch-Carlson interpolation