说明：  用MATLAB作非线性最小二乘拟合 Matlab的提供了两个求非线性最小二乘拟合的函数：lsqcurvefit和lsqnonlin。
(Use MATLAB for nonlinear least squares fitting, MATLAB provides two nonlinear least-square fitting function: lsqcurvefit and lsqnonlin. )