Python/maths/tanh.py

"""
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
import numpy as np
import doctest


def tanh_func(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:
        >>> tanh_func(np.array([1, 5, 6, 113, 13, 16, -5.23]))
        array([ 0.76159416,  0.9999092 ,  0.99998771,  1.        ,  1.        ,
            1.        , -0.99994268])

    """

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


if __name__ == '__main__':
    doctest.testmod()