Algorithms [Sedgewick, Robert]

used for this type of application. The idea is fundamentally the same; the problem is that the derivatives may not be easy to compute. What is used is an iterative method: use some estimate for the coefficients, then use these within the method of least squares to compute the derivatives, thus producing a better estimate for the coefficients. This basic method, which is widely used today, was outlined by Gauss in the 1820s.