The ELU activation is added (#8699)

* tanh function been added

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* tanh function is added

* tanh function is added

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* tanh function added

* tanh function added

* tanh function is added

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* ELU activation function is added

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* elu activation is added

* ELU activation is added

* Update maths/elu_activation.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Exponential_linear_unit activation is added

* Exponential_linear_unit activation is added

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Co-authored-by: Christian Clauss <cclauss@me.com>
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"""
Implements the Exponential Linear Unit or ELU function.
The function takes a vector of K real numbers and a real number alpha as
input and then applies the ELU function to each element of the vector.
Script inspired from its corresponding Wikipedia article
https://en.wikipedia.org/wiki/Rectifier_(neural_networks)
"""
import numpy as np
def exponential_linear_unit(vector: np.ndarray, alpha: float) -> np.ndarray:
"""
Implements the ELU activation function.
Parameters:
vector: the array containing input of elu activation
alpha: hyper-parameter
return:
elu (np.array): The input numpy array after applying elu.
Mathematically, f(x) = x, x>0 else (alpha * (e^x -1)), x<=0, alpha >=0
Examples:
>>> exponential_linear_unit(vector=np.array([2.3,0.6,-2,-3.8]), alpha=0.3)
array([ 2.3 , 0.6 , -0.25939942, -0.29328877])
>>> exponential_linear_unit(vector=np.array([-9.2,-0.3,0.45,-4.56]), alpha=0.067)
array([-0.06699323, -0.01736518, 0.45 , -0.06629904])
"""
return np.where(vector > 0, vector, (alpha * (np.exp(vector) - 1)))
if __name__ == "__main__":
import doctest
doctest.testmod()