r = y - ŷ = (1- H) y Weighted Least Squares It is usually assumed that the response data is of equal quality and, therefore, has constant variance. If this assumption is violated, your fit might be unduly influenced by data of poor quality. aq=interp1 (x, a, xq, method): Here we can change the interpolation method, which we will discuss later. There are many interpolation methods like nearest, linear, next, previous, cubic, v5cubic, pchip, spline or makima. The default method used is always linear. aq=interp1 (x, a, xq, method, extrapolation method): Extrapolation can be defined. Nonlinear least squares regression extends linear least squares regression for use with a much larger and more general class of functions. Almost any function that can be written in closed form can be incorporated in a nonlinear regression model. Unlike linear regression, there are very few limitations on the way parameters can be used in the. Pure MATLAB solution (No toolboxes) In order to perform nonlinear least squares curve fitting, you need to minimise the squares of the residuals. This means you need a minimisation routine. Basic MATLAB comes with the fminsearch function which is based on the Nelder-Mead simplex method. Potential flow matlab code.