logrange.cpp

利用拉格朗日、牛顿插值法解方程组

// Logrange.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include"fstream.h"
#include"iostream.h"
#include"iomanip.h"

class LogR
{
protected:
	int n;
	double *XI;
	double *YI;
	double x;
public:
	LogR(char *file_name);
	void print_result();
};

LogR::LogR(char *file_name)
{
	ifstream input(file_name);
	
	input>>n;
	XI=new double[n+1];
	YI=new double[n+1];
	for(int i=0;i<=n;i++)
		input>>XI[i]>>YI[i];
	input>>x;
}
void LogR::print_result()
{
	double sum;
	double temp;
	sum=0;
	for(int i=0;i<n+1;i++)
	{
		temp=1;
		for(int j=0;j<n+1;j++)
			if(j!=i)
				temp*=(x-XI[j])/(XI[i]-XI[j]);
		sum+=temp*YI[i];
	}

	cout<<"结果为:  "<<setiosflags(ios::fixed)<<setprecision(6)<<sum<<endl;
}

void main()
{
	LogR  logr("a.txt");
	logr.print_result();
}