Wrong formula for TANH squashing function

[wagenaartje]

No, it is correct. Integrate it yourself to see why, or have a look at these sources:

• https://en.wikipedia.org/wiki/Activation_function
• http://math2.org/math/derivatives/more/hyperbolics.htm
• https://math.stackexchange.com/questions/741050/hyperbolic-functions-derivative-of-tanh-x (see this one for proof)

If using cosh, it should be written as follows:

return 1/Math.pow(Math.cosh(x), 2)

But

return 1 - Math.exp(Math.tanh(x), 2)

Is just the same thing.