C语言实现拉格朗日插值法

//POINTS.h
#pragma once
#include<vector>
using namespace std;
#ifndef _POINTS_
#define _POINTS_
class POINTS
{
public:
  typedef struct MYPOINT
  {
    double x;
    double y;
  }mypoint;
  int len;
  int size;
  virtual void run(double val);
  virtual void loaddata(double* vallist);
};
#endif // !_POINTS_
 

//POINTS.cpp
#include "POINTS.h"
#include<iostream>
using namespace std;
void POINTS::run(double val)
{
  cout << "计算函数" << endl;
}
void POINTS::loaddata(double* vallist)
{
  cout << "数据处理函数" << endl;
}

//LAGRANGE.h
#pragma once
#include "POINTS.h"
#ifndef _LAGRANGE_
#define _LAGRANGE_
class LAGRANGE :
    public POINTS
{
public:
    LAGRANGE(int n);
    vector<mypoint> datalist;
    virtual void run(double val);
    virtual void loaddata(double* vallist);
};
#endif // !LAGRANGE

//LAGRANGE.cpp
#include "LAGRANGE.h"
#include<iostream>
using namespace std;
LAGRANGE::LAGRANGE(int n)
  :datalist(n)
{
  this->size = n;
  this->len = 0;
}
void LAGRANGE::run(double val)
{
  double sum = 0.0;
  vector<double> templist;
  for (size_t i = 0; i < this->size; i++)
  {
    double tempval = 1.0;
    for (size_t j = 0; j < this->size; j++)
    {
      if (j != i)
        tempval *= ((val - this->datalist.at(j).x) /
          (this->datalist.at(i).x - this->datalist.at(j).x));
      else
        continue;
    }
    templist.push_back(tempval);
  }
  for (size_t i = 0; i < this->size; i++)
  {
    sum += this->datalist.at(i).y * templist.at(i);
  }
  cout << "拉格朗日" << this->size << "项插值计算为：" << sum << endl;
}
 
void LAGRANGE::loaddata(double* vallist)
{
  cout << "正在处理数据..." << endl;
  for (size_t i = 0; i < this->size * 2; i++)
  {
    if (((i + 1) % 2) == 0)
    {
      this->datalist.at(this->len).y = vallist[i];
      this->len++;
    }
    else
    {
      this->datalist.at(this->len).x = vallist[i];
    }
    
  }
}

//main.cpp
#include<iostream>
#include"POINTS.h"
#include"LAGRANGE.h"
using namespace std;
int main()
{
  cout << "例1" << endl;
  //实例化工具类
  LAGRANGE lgr(2);
  //构建运算参数表
  double val[4] = { 100.0,10.0,121.0,11.0 };
  //调用处理数据函数
  lgr.loaddata(val);
  //传入目标x运算,例1
  lgr.run(115);
  //传入目标x运算,例2
  cout << "例2" << endl;
  LAGRANGE lgr1(3);
  double val1[6] = { 100.0,10.0,121.0,11.0,144.0,12.0 };
  lgr1.loaddata(val1);
  lgr1.run(115);
  //课上的题目求ln3.16
  cout << "求ln3.16" << endl;
  LAGRANGE lgr2(2);
  double val2[4] = { 3.1,1.1314,3.2,1.1632 };
  lgr2.loaddata(val2);
  lgr2.run(3.16);
  system("pause");
  return 0;
}