说明：  非线性最小二乘法，Levenberg-Marquardt算法，很详细的理论推导，讲解。对研究最小二乘法和Levenberg-Marquardt算法的同学有很大的帮助！
(Nonlinear least squares method, Levenberg-Marquardt algorithm, a very detailed theoretical analysis to explain. The study of least squares and Levenberg-Marquardt algorithm is very helpful to the students!)