Question

And no, this does not (to my understanding) involve integer division or floating-point rounding issues.

My exact code is:

    static void Main(string[] args)
    {
        double power = (double)1.0 / (double)7.0;
        double expBase = -128.0;
        System.Console.WriteLine("sanity check: expected: -128 ^ 0.142857142857143 = -2.    actual: " + expBase + " ^ " + power + " = " + Math.Pow(expBase, power));
        System.Console.ReadLine();
    }

The output is:

sanity check: expected: -128 ^ 0.142857142857143 = -2.    actual: -128 ^ 0.14285
7142857143 = NaN

The Target Framework for this code is (according to solution properties) .NET Framework 4.0 Client Profile.

Strangely I haven’t found any mention of this anywhere on the Web. Am I taking crazy pills here!?

Answer 1

Seems to be exactly as specified; from the Math.Pow() remarks section on Pow(x,y);

Parameters
x < 0 but not NegativeInfinity; y is not an integer, NegativeInfinity, or PositiveInfinity.

Result
NaN