GoldenSection

using System;

public class GoldenSectionMethod
{
    public static readonly double Phi = (1 + Math.Sqrt(5)) / 2;
    public readonly double Accuracy;

    public readonly Func<double, double> Func;

    public GoldenSectionMethod(Func<double, double> func, double accuracy = 0.01)
    {
        if (func is null)
            throw new Exception("Function is null");

        if (accuracy <= 0)
            throw new Exception("Wrong accuracy");

        Func = func;
        Accuracy = accuracy;
    }

    public double FindMin(double start, double end)
    {
        int counter = 0;
        while (Math.Abs(end - start) >= Accuracy)
        {
            var x1 = end - (end - start) / Phi;
            var x2 = start + (end - start) / Phi;

            if (Func(x1) >= Func(x2))
                start = x1;
            else
                end = x2;
            counter++;
        }

        Console.WriteLine($"Number of iterations for the First Part of GoldenSection method {counter} ");
        return (start + end) / 2;
    }
}