Where's the inverse of Math.tanh in the math libraries?

Question

y = Math.Tanh(x) is the hyperbolic tangent of x. But I need f(y) = x. For the regular tangent there\'s Arctan, but where\'s Arctanh?

Answer 1

Why don't you implement one by yourself? You can find the equation e.g. here and tt's not that difficult:

public static class MyMath
{
    public static double Arctanh(double x)
    {
        if (Math.Abs(x) > 1)
            throw new ArgumentException("x");

        return 0.5 * Math.Log((1 + x) / (1 - x));
    }
}

Answer 2

I don't think the C# libraries include the arc hyperbolic trig functions, but they're easy to compute:

atanh(x) = (log(1+x) - log(1-x))/2

In C#:

public static double ATanh(double x)
{
    return (Math.Log(1 + x) - Math.Log(1 - x))/2;
}

Answer 3

the Inverse HTangent is can be calc by doing Log((1 + X) / (1 – X)) / 2

Answer 4

I installed MathNet from the package manager. It has MathNet.Numerics.Trig.InverseHyperbolicTangent(x) which works well enough.