线性插值 二次插值 拉格郎日插值

#include
#include
using namespace std;

void Linear_interpolation(double *x, double *y, double input);//分段线性插值
void Quadratic_interpolation(double *x,double *y,double u);//分段二次插值
void Lagrange_interpolation(double *x, double *y, double xx);//拉格郎日插值

int main()//主函数
{
	double x[6]={0.0, 0.1, 0.195, 0.3, 0.401, 0.5};
	double y[6]={0.39894, 0.39695, 0.39142, 0.38138, 0.36812, 0.35206};
	double u;
	while(cin>>u)
	{
		Linear_interpolation(x,y,u); //分段线性插值  
		Quadratic_interpolation(x,y,u); //分段二次插值
		Lagrange_interpolation(x,y,u); //拉格郎日插值
	}  	  
	 
}

void Linear_interpolation(double *x, double *y, double input)//分段线性插值
{
	double output;   
	for (int i=0;i<5;i++)  
	{  
		if (x[i] <= input && x[i+1] >= input)  
		{  
			output=y[i] +(y[i+1]-y[i])*(input-x[i])/(x[i+1]-x[i]);  
			break;  
		}  
	}  
    cout<<"Linear_interpolation: "<fabs(u-x[i+1]))  
		{  
			k=i;  
			v=y[k]*(u-x[k+1])*(u-x[k+2])/((x[k]-x[k+1])*(x[k]-x[k+2]))+y[k+1]*(u-x[k])*(u-x[k+2])/((x[k+1]-x[k])*(x[k+1]-x[k+2]))+y[k+2]*(u-x[k])*(u-x[k+1])/((x[k+2]-x[k])*(x[k+2]-x[k+1]));  
		}  
		if(u>x[4])  
		{  
			k=3;  
			v=y[k]*(u-x[k+1])*(u-x[k+2])/((x[k]-x[k+1])*(x[k]-x[k+2]))+y[k+1]*(u-x[k])*(u-x[k+2])/((x[k+1]-x[k])*(x[k+1]-x[k+2]))+y[k+2]*(u-x[k])*(u-x[k+1])/((x[k+2]-x[k])*(x[k+2]-x[k+1]));  
		}  
	}  
    cout<<"Quadratic_interpolation: "<