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代码说明：

//=== === === === === === === = //函数说明 //函数名称：PolyFit //函数功能：最小二乘法曲线拟合 //使用方法：double *x ---- 存放n个数据点的X坐标 // double *y ---- 存放n个数据点的Y坐标 // int n -------- 给定数据点个数 // double *a ---- 返回m-1次拟合多项式的m个系数 // int m -------- 拟合多项式的项数，即拟合多项式的最高次为m-1。要求m20，则本函数自动按m=min{n,20}处理 // double *dt --- dt[0]返回拟合多项式与各数据点误差的平方和；dt[1]返回拟合多 // 项式与各数据点的误差绝对值之和；dt[2]返回拟合多项式与各数据 // 点误差绝对值的最大值 //注意事项：拟合多项式的形式为 y = b0 + b1*(x-Xavr)... -//=== === === === === ==== === === === === === === ==== === =// function annotations// function name : PolyFit// Function functions : Least Squares Curve Fitting// Use : double* x n-store data point coordinates of the X//* y double-storage n data point Y coordinates// int n-------- given the number of data points//* a double---- returned to the m-1 m fit polynomial coefficients// int m-------- polynomial fitting items , which is the highest polynomial fitting time for m-1. Request m