add relu function (#1795)

maths/relu.py

@@ -0,0 +1,39 @@
+"""
+This script demonstrates the implementation of the ReLU function.
+
+It's a kind of activation function defined as the positive part of its argument in the context of neural network.
+The function takes a vector of K real numbers as input and then argmax(x, 0).
+After through ReLU, the element of the vector always 0 or real number.
+
+Script inspired from its corresponding Wikipedia article
+https://en.wikipedia.org/wiki/Rectifier_(neural_networks)
+"""
+
+import numpy as np
+from typing import List
+
+
+def relu(vector: List[float]):
+    """
+        Implements the relu function
+
+        Parameters:
+            vector (np.array,list,tuple): A  numpy array of shape (1,n)
+            consisting of real values or a similar list,tuple
+
+
+        Returns:
+            relu_vec (np.array): The input numpy array, after applying
+            relu.
+
+        >>> vec = np.array([-1, 0, 5])
+        >>> relu(vec)
+        array([0, 0, 5])
+    """
+
+    # compare two arrays and then return element-wise maxima.
+    return np.maximum(0, vector)
+
+
+if __name__ == "__main__":
+    print(np.array(relu([-1, 0, 5])))  # --> [0, 0, 5]