C语言实现最小二乘法拟合曲线，结合高斯消元法

/*
    本实验根据数组x[], y[]列出的一组数据，用最小二乘法求它的拟合曲线。
    近似解析表达式为y = a0 + a1 * x + a2 * x^2 + a3 * x^3;
*/
#include <stdio.h>
#include <math.h>

#define maxn 9
#define rank_ 3

int main(){
   // double x[maxn] = {0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55};
   // double y[maxn] = {0, 1.27, 2.16, 2.86, 3.44, 3.87, 4.15, 4.37, 4.51, 4.58, 4.02, 4.64};
  double x[maxn] = {0, 0.3, 0.9, 1.2, 1.6, 2, 2.5, 3};
      double y[maxn] = {0.00515, 0.02125, 0.055, 0.0725, 0.09675, 0.12195, 0.1549, 0.1897, 0.3483};
    double atemp[2 * (rank_ + 1)] = {0}, b[rank_ + 1] = {0}, a[rank_ + 1][rank_ + 1];
    int i, j, k;

    for(i = 0; i < maxn; i++){  //
        atemp[1] += x[i];
        atemp[2] += pow(x[i], 2);
        atemp[3] += pow(x[i], 3);
        atemp[4] += pow(x[i], 4);
        atemp[5] += pow(x[i], 5);
        atemp[6] += pow(x[i], 6);
        b[0] += y[i];
        b[1] += x[i] *  y[i];
        b[2] += pow(x[i], 2) * y[i];
        b[3] += pow(x[i], 3) * y[i];
    }