C++实现最小二乘法对y=exp(x)的二次拟合

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#include<iostream>#include<math.h>const int N=20;const int n=3;double A[n][n];double B[n];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[n][n];////double B[n];////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[N][N]={{10,-1.0,-2.0},{-1.0,10.0,-2.0},{-1.0,-1.0,5.0}};   //   double B[N]={72,83,42};      double X[N]={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;  }

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