histogram and normal probability plot to check for skewness or other non-normality in the residuals. Extensions A different method consists in transforming the non-linear regression to a linear regression thanks to a convenient integral equation. Then, there is no need for initial guess and no need for iterative process : the fitting is directly obtained. See also Pitch detection algorithm Spectral density estimation#Single tone References External links Beam deflection case study Regression with time series structure Regression models