Lagranzh

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace interpolationLagranzh
{
    class Program
    {
        static double func(double x)
        {
            return Math.Log(x)+Math.Cosh(Math.Atan(x));
        }
        static double InterpolateLagrange(double x, double[] x_values, double[] y_values, int size)
        {
            double lagrange_pol = 0;
            double basics_pol;

            for (int i = 0; i < size; i++)
            {
                basics_pol = 1;
                for (int j = 0; j < size; j++)
                {
                    if (j == i) continue;
                    basics_pol *= ((x - x_values[j]) / (x_values[i] - x_values[j]));
                }
                lagrange_pol += (basics_pol * y_values[i]);
            }
            return lagrange_pol;
        }
        static string pathIn = @"F:\ИТМО\2 курс\ВМ\interpolationLagranzh\interpolationLagranzh\IO\input.txt";
        //static string pathOut = @"F:\ИТМО\2 курс\ВМ\interpolationLagranzh\interpolationLagranzh\IO\output.xlx";
        static int n = 10;
        static double[] x = new double[n];
        static double[] y = new double[n];
        static void Main(string[] args)
        {
            #region Writer
            using (StreamWriter sw = new StreamWriter(pathIn))
            {
                for (int i = 1; i <= n; i++)
                {
                    sw.WriteLine(i + "\t" + func(i));
                }
            }
            #endregion
            #region Reader
            using (StreamReader sr = new StreamReader(pathIn))
            {
                for (int i = 1; i <= n; i++)
                {
                    string[] s = sr.ReadLine().Split('\t');
                    x[i - 1] = double.Parse(s[0]);
                    y[i - 1] = double.Parse(s[1]);

                }
            }
            #endregion
                for (double i = 1; i <= 10; i += 0.1)
                {
                    double InterpolateLagrange_ans = InterpolateLagrange(i, x, y, n);
                    double theory = func(i);
                    Console.WriteLine("x = {0:0.0}  Lagr ={1:0.000000} Correct = {2:0.000000} delta = {3}", i, InterpolateLagrange_ans, func(i), (InterpolateLagrange_ans - theory));
                }




                Console.ReadKey();
        }
    }
}