c2.cpp

来自「数值分析最常用的四十种算法」· C++ 代码 · 共 36 行

//C2
//Interpolate,using Langrang Methom

#include <iostream.h>
#include <time.h>

//Langrange polynomial
double LP(double x,double *ax,double *ay,int n)
{
	double sum=0,Tsum=1;
	int i,j;
	for (i=0;i<n;i++)
	{
		for (j=0;j<n;j++)
		{
			if (j!=i)
				Tsum=Tsum*(x-ax[j])/(ax[i]-ax[j]);
		}
		sum=sum+Tsum*ay[i];
		Tsum=1;
	}
	return sum;
}

void main()
{
	double ax[]={0.56160,0.56280,0.56401,0.56521},ay[]={0.82741,0.82659,0.82577,0.82495},x=0.5635;
	int n=4;
	cout<<"The value at that point is: "<<LP(x,ax,ay,n)<<endl;
	cin>>n;
}

//运行结果：0.826116,Lagrange实现并不困难，
//但如要改变节点数，将会带来非常多的麻烦