"""
This script demonstrates the implementation of the tangent hyperbolic
or tanh function.

The function takes a vector of K real numbers as input and
then (e^x - e^(-x))/(e^x + e^(-x)). After through tanh, the
element of the vector mostly -1 between 1.

Script inspired from its corresponding Wikipedia article
https://en.wikipedia.org/wiki/Activation_function
"""
import numpy as np


def tangent_hyperbolic(vector: np.array) -> np.array:
    """
        Implements the tanh function

        Parameters:
            vector: np.array

        Returns:
            tanh (np.array): The input numpy array  after applying
        tanh.

        mathematically (e^x - e^(-x))/(e^x + e^(-x)) can be written as (2/(1+e^(-2x))-1

    Examples:
        >>> tangent_hyperbolic(np.array([1,5,6,-0.67]))
        array([ 0.76159416,  0.9999092 ,  0.99998771, -0.58497988])

    """

    exp_vector = np.exp(-2 * vector)
    return (2 / (1 + exp_vector)) - 1


if __name__ == "__main__":
    import doctest

    doctest.testmod()