Least-squares fit by a function linear in the parameters

Following the approach on page 266 from the book "Probability and statistics in particle physics" by A.G. Frodesen, O. Skgeggestad and H. Tofte, the parameters from the least squares fit by a function linear in the parameters (for example a straight line or any polynomial, a sine function if only the amplitude and/or offset are fitted and not the frequency nor the phase) are obtained, together with the covariance matrix of those parameters, the chi squared and the p-value. Four examples (straight line, parabola, fit by polynomials from the Legendre basis and ampltude and offset of a sine function) are provided in a different script.