#include <iostream>
#include <cmath>
#include <fstream>

using namespace std;

const int number_of_points = 3000;
const int point_of_start_internal_condition = number_of_points / 3;
const int border_of_internal_condition = number_of_points / 10;
double upper_diagonal[number_of_points];
double lower_diagonal[number_of_points];
double main_diagonal[number_of_points];
double external_function[number_of_points];
double intial_conditions[number_of_points];

void create_approximation () {
    for (int i = 0; i < number_of_points; i++) {
        ::upper_diagonal[i] = 1;
        ::lower_diagonal[i] = 1;
        ::main_diagonal[i] = -2;
        ::external_function[i] = 0;
        ::intial_conditions[i] = 0;
    }
    ::upper_diagonal[number_of_points - 1] = 0;
    ::lower_diagonal[0] = 0;
    ::main_diagonal[0] = -1;
    ::main_diagonal[number_of_points - 1] -= (1 / 2 + 1 / number_of_points) / (1 / 2 - 1 / number_of_points);
    ::external_function[0] = -1 / number_of_points;
    for (int i = point_of_start_internal_condition - border_of_internal_condition; i < point_of_start_internal_condition + border_of_internal_condition + 1; i++) {
        intial_conditions[i] = 1;
    }
}

void multiplication_3dig_matrix_on_vector (int dim, double *lower_diagonal, double *main_diagonal, double *upper_diagonal, double *result) {
    for (int i = 0; i < dim; i++) {
        result[i] = lower_diagonal[i] + main_diagonal[i] + upper_diagonal[i];
    }
}