I am currently studying the methods which are used to fit nonlinear models while studying them I found one great method is splined . I found two types of splines one is cubic splines and is natural cubic splines .

**cubic splines**- A cubic spline is a spline constructed of piecewise third-order polynomials which pass through a set of control points. The second derivative of each polynomial is commonly set to zero at the endpoints since this provides a boundary condition that completes the system of equations.

**natural cubic splines** - A natural cubic spline extrapolates linearly beyond the boundary knots.

I want to know which one of them is the better one and why