用于信号的周期成分提取，使用的最小二乘方法，拟合出一个单频的正弦信号。(For the extraction of periodic components of signals, the least square method is used to fit a sinusoidal signal of a single frequency.)

用最小二乘法对时间序列进行周期拟合，求出周期曲线的参数，并求出拟合的精度评价。(The least square method is used to fit the time series, the parameters of the periodic curve are obtained, and the accuracy of the fitting is evaluated.)