C++实现最小二乘法对y=exp(x)的二次拟合

#include<iostream>
#include<math.h>
const int N=20;
const int n=3;
double A

;
double B
;
double start=0, end=1.0;//积分范围
const double PI=3.1415926;
using namespace std;
void HibertMatrix();
double func1(double x);
double func2(double x);
void projectAarry();
void jacobi();
int main()
{
////double A

;
////double B
;
////double start=0, end=1.0;//积分范围
HibertMatrix(); //生成希尔伯特矩阵
projectAarry();//生成投影矩阵
jacobi();//求解正规方程
return 0;
}
void HibertMatrix()//希尔伯特矩阵的生成
{
for(int i=0;i<n;i++)
for(int j=0;j<n;j++)
A[i][j]=1.0/(i+j+1);
}
double func1(double x)    //Expansion function
{
return exp(x);
}
double func2(double x)  //Base function
{
return x;

}
void projectAarry()
{
double h=(end-start)/N;
for(int i=0;i<n;i++)
{
B[i]=(pow(func2(start),i)*func1(start)+pow(func2(end),i)*func1(end))*h/2;
for(int k=1;k<N;k++)
B[i]+=pow(func2(start+k*h),i)*func1(start+k*h)*h;
cout<<B[i]<<'\t';
}
cout<<endl;
}
void jacobi()
{

//	  double A

={{10,-1.0,-2.0},{-1.0,10.0,-2.0},{-1.0,-1.0,5.0}};
//   double B
={72,83,42};
double X
={0,0,0,};
for (int k=0;k<100;k++)
{
for(int i=0;i<n;i++)
{
double sum=0;
for(int j=0;j<n;j++)
{
if(j==i) continue;
sum+=A[i][j]*X[j];
}
X[i]=(B[i]-sum)/A[i][i];
}
}
for (int i=0;i<n;i++)
cout<<X[i]<<'\t';
cout<<endl;
}