Task №3

#include "stdafx.h"
#include "iostream"
#include "cmath"
#include <iomanip>
using namespace std;
#define PI 3.141592653589793238463
double Lagrange (double t, int n, double *x, double *y)
{
    double L=0;
    double *l = new double [n+1];
    for( int i=0;i<=n;i++)
    {
        l[i]=1;
        for(int j=0;j<=n;j++)
        {
            if(i==j)
                continue;
            else
                l[i]*=(t-x[j])/(x[i]-x[j]);
        }
    }
    for (int k=0;k<=n;k++)
        L+=(l[k]*y[k]);
    return L;
}

int _tmain(int argc, _TCHAR* argv[])
{
    int n;
    double a,b;
    cout<<"ENTER a: ";
    cin>>a;
    cout<<"ENTER b: ";
    cin>>b;
    cout<<"ENTER n: ";
    cin>>n;
    double *t = new double [n+1];
    double *x = new double [n+1];
    double *y = new double [n+1];
    for(int i=0;i<=n;i++)
        t[i]=cos(PI*(2*i+1)/(2*n+2));

    for(int i=0;i<=n;i++)
    {
        x[i]=(a+b)/2+t[i]*(b-a)/2;
        y[i]=fabs(x[i]);
        cout<<x[i]<<"\t"<<y[i]<<endl;
    }
    cout<<endl;

    for(int i=0;i<n;i++)
    {
        cout<<Lagrange(x[i], n, x, y)<<endl;
        cout<<"\t"<<Lagrange((x[i+1]+x[i])/2, n, x, y)<<endl;
    }

    system ("pause");
    return 0;
}