两种对二阶系统进行参数辨识的最小二乘算法，一种可以直接得到输入输出之间的传递函数，一种可以解出线性的差分方程各系数，再反解得到传递函数。附带的一个二阶系统的模型，可以自行下载导入输入输出数据进行试验。(Two kinds of least square algorithm for parameter identification of second-order system, one can directly get the transfer function between input and output, the other can solve the coefficients of linear difference equation, and then get the transfer function by inverse solution. The attached model of a second-order system can download the input and output data for test.)