Question

private double f(double x, double zn = 1)
    {
        double X = - zn;
        X *= x * x * (x + 1);
        X *= Math.Pow((x - 2), 0.333);
        return funct ? x : X;
    }

I have this code. When I try to find Math.Pow((x-2), 0.333) – i have NaN.
How to solve it? Why NaN?

Rewritten…

private double f(double x, double zn = 1)
    {
        double answer = - zn;
        answer *= x * x * (x + 1);
        answer *= Math.Pow((x - 2), 0.333);
        return answer;
    }

Answer 1

My guess is that you’re taking the cube root of a negative number. That seems the most likely cause, but your code is really hard to read due to having both x and X as local variables…

After closer examination, as you’re not actually modifying x at any point, it really depends on the incoming value of x. If it’s a finite value greater than or equal to 2, it should be fine. But if x is smaller than 2, it will fail (well, return NaN) for reasons of simple maths…