Efficient Implementation of a Variable Projection Algorithm for Nonlinear Least Squares Problems Nonlinear least squares frequently arise for which the variables to be solved for can be separated into a linear and a nonlinear part. A variable projection algorithm has been developed recently which is designed to take advantage of the structure of a problem whose variables separate in this way. This paper gives a slightly more efficient and slightly more general version of this algorithm than has appeared earlier. CACM March, 1974 Krogh, F. T. nonlinear least squares, parameter estimation, variable projection 5.14 5.15 CA740313 JB January 18, 1978 10:49 AM 2670 5 2670 2670 5 2670 2670 5 2670