метод прогонки

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include<chrono>
#include<random>


#define forn(i, n) for(int i = 0; i < int(n); i++)
using namespace std;
const int V = 10;//variant
const int n = 4;
const double k = 1e-2;
using namespace std;

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

void boost()
{
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
}
vector< vector< double > > A(n);
vector<double> B(n);


void init() {
    forn(i, n)
        A[i].resize(n);
    forn(i, n)
        for (int j = max(0, i - 1); j < min(i + 2, n); ++j)
        {
            A[i][j] = i * j + i + rnd()%11;
        }
    forn(i, n)
        B[i] = rnd() % 23;
}
void print()
{
    forn(i, n) {
        forn(j, n)
            cout << A[i][j] << "\t";
        cout << endl;
    }
    for (auto v : B)
        cout << v << " ";
    cout << endl;
}


vector<double> sweepMetod()
{

    int N = n - 1;
    double y, p[n], q[n], matRes[n];
    y = A[0][0];
    p[0] = -A[0][1] / y;
    q[0] = B[0] / y;
    for (int i = 1; i < N; ++i)
    {
        y = A[i][i] + A[i][i - 1] * p[i - 1];
        p[i] = -A[i][i + 1] / y;
        q[i] = (B[i] - A[i][i - 1] * q[i - 1]) / y;
    }

    vector<double> res(n);
    res[N] = (B[N] - A[N][N - 1] * q[N - 1])
        / (A[N][N] + A[N][N - 1] * p[N - 1]);
    for (int i = N - 1; i >= 0; i--)
        res[i] = p[i] * res[i + 1] + q[i];
    return res;

}
void input()
{
    forn(i, n)
        forn(j, n)
        cin >> A[i][j];
    forn(i, n)
        cin >> B[i];
}

int main()
{
    boost();
    init();
    //input();
    print();
    vector<double> ans = sweepMetod();
    for (auto v : ans)
        cout << v << " ";
}