Added Softmax to Maths folder (#516)

DIRECTORY.md

@@ -119,6 +119,7 @@
   * [PrimeCheck](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/PrimeCheck.js)
   * [ReversePolishNotation](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/ReversePolishNotation.js)
   * [SieveOfEratosthenes](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/SieveOfEratosthenes.js)
+  * [Softmax](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/Softmax.js)
   * test
     * [Abs](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/Abs.test.js)
     * [Area](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/Area.test.js)
@@ -145,6 +146,7 @@
     * [PrimeCheck](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/PrimeCheck.test.js)
     * [ReversePolishNotation](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/ReversePolishNotation.test.js)
     * [SieveOfEratosthenes](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/SieveOfEratosthenes.test.js)
+    * [Softmax](https://github.com/TheAlgorithms/Javascript/blob/master/Maths/test/Softmax.test.js)
 
 ## Navigation
   * [Haversine](https://github.com/TheAlgorithms/Javascript/blob/master/Navigation/Haversine.js)

Maths/Softmax.js

@@ -0,0 +1,13 @@
+// Wikipedia: https://en.wikipedia.org/wiki/Softmax_function
+
+const Softmax = (inputs) => {
+  const eulerExpOfAllInputs = inputs.map(input => Math.exp(input))
+  const sumOfEulerExpOfAllInputs = eulerExpOfAllInputs.reduce((a, b) => a + b)
+
+  return inputs.map((input) => {
+    const eulerExpInputs = Math.exp(input)
+    return eulerExpInputs / sumOfEulerExpOfAllInputs
+  })
+}
+
+export { Softmax }

Maths/test/Softmax.test.js

@@ -0,0 +1,12 @@
+import { Softmax } from '../Softmax'
+
+describe('Softmax', () => {
+  it('should return equal distribution of 1 for equal input values', () => {
+    expect(Softmax([1, 1])).toEqual([0.5, 0.5])
+    expect(Softmax([1, 1, 1, 1])).toEqual([0.25, 0.25, 0.25, 0.25])
+  })
+
+  it('should return values which sum to the value of 1', () => {
+    expect(Softmax([1, 2, 3, 4]).reduce((a, b) => a + b, 0)).toEqual(1)
+  })
+})