// ConsoleApplication2.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <cstdio>
#include <cfloat>
#include <cmath>
#include <utility>

using namespace std;

void mult_mat_vec(double* mat, double* vec, double* res, int n) {
    for (int i = 0; i < n; i++) {
        res[i] = 0;
        for (int j = 0; j < n; j++) {
            res[i] += mat[i * n + j] * vec[j];
        }
    }
}

double l_inf_dist(double* v1, double* v2, int n) {
    double res = DBL_MIN;
    for (int i = 0; i < n; i++) {
        double diff = fabs(v1[i] - v2[i]);
        res = (diff > res) ? diff : res;
    }
    return res;
}

void div_vec(double* v1, double* v2, double* res, int n) {
    for (int i = 0; i < n; i++) {
        res[i] = v1[i] / v2[i];
    }
}

double eigen(double* mat, double* mem, int n, double eps = 1e-8) {
    double* y0 = mem;
    double* y1 = mem + n;
    double* y = mem + 2 * n;
    double* y_prev = mem + 3 * n;

    for (int i = 0; i < n; i++) {
        y0[i] = 1;
        y_prev[i] = DBL_MAX;
    }

    while (true) {
        mult_mat_vec(mat, y0, y1, n);
        div_vec(y1, y0, y, n);
        if (l_inf_dist(y, y_prev, n) < eps) {
            return y[0] / y_prev[0];
        }
        swap(y0, y1);
        swap(y, y_prev);
    }
}

void print_vec(double* vec, int n) {
    for (int i = 0; i < n; i++) {
        printf("%.4f ", vec[i]);
    }
}

void gen_test_mat(double* mat, int n) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (i == j) {
                mat[i * n + j] = n + i;
            } else {
                mat[i * n + j] = n * n * (i + j);
            }
        }
    }
}

double A[] = {
    1, 0, 0,
    0, 1, 0,
    0, 0, 1
};

double V[] = { 1, 2, 3 };

int _tmain(int argc, _TCHAR* argv[])
{
    const int n = 3;

    double mem[4 * n] = { 0 };

    gen_test_mat(A, n);

    printf("Answer: %.8f", eigen(A, mem, n));

    scanf_s("Press any key");

    return 0;
}