FibonacciMethod

#include <algorithm>
#include <iostream>
#include <vector>
#include <cmath>
#include <exception>

int64_t fib(int64_t n)
{
    if (n == 0 || n == 1)
        return 1;
    int64_t a = 1, b = 1, res = 0;
    for (int64_t i = 1; i < n; ++i)
    {
        res = a + b;
        a = b;
        b = res;
    }
    return res;
}

double fibonacci(double a, double b, double (*f)(double x), int64_t n)
{
    if (a > b)
        std::swap(a, b);
    double lambda, mu;
    int64_t fibo;
    for (int64_t k = 0; k < n; ++k)
    {
        fibo = fib(n - k + 1);
        lambda = a + (double)(fib(n - k - 1)) / fibo * (b - a);
        mu = a + (double)(fib(n - k)) / fibo * (b - a);

        if (f(lambda) > f(mu))
        {
            a = lambda;
        }
        else
        {
            b = mu;
        }
    }
    return (a + b) * 0.5;
}