The tanh activation function is added (#8689)

* tanh function been added

* tanh function been added

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* tanh function is added

* tanh function is added

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* tanh function added

* tanh function added

* tanh function is added

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

maths/tanh.py

@@ -0,0 +1,42 @@
+"""
+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])
+
+        >>> tangent_hyperbolic(np.array([8,10,2,-0.98,13]))
+        array([ 0.99999977,  1.        ,  0.96402758, -0.7530659 ,  1.        ])
+
+    """
+
+    return (2 / (1 + np.exp(-2 * vector))) - 1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()