Added function and test cases for cross-entropy loss (aimacode#853)

* Correction in the formula for mean square error

* Added cross-entropy loss

* Test case for cross-entropy loss

* Decimal point mistake

* Added spaces around = and ==

Author: krishnaw14

learning.py

@@ -21,6 +21,10 @@
 def euclidean_distance(X, Y):
     return math.sqrt(sum((x - y)**2 for x, y in zip(X, Y)))
 
+def cross_entropy_loss(X,Y):
+    n=len(X)
+    return (-1.0/n)*sum(x*math.log(y)+(1-x)*math.log(1-y) for x,y in zip(X,Y) )
+
 
 def rms_error(X, Y):
     return math.sqrt(ms_error(X, Y))

tests/test_learning.py

@@ -18,6 +18,16 @@ def test_euclidean():
     distance = euclidean_distance([0, 0, 0], [0, 0, 0])
     assert distance == 0
 
+def test_cross_entropy():
+    loss = cross_entropy_loss([1,0], [0.9, 0.3])
+    assert round(loss,2) == 0.23
+
+    loss = cross_entropy_loss([1,0,0,1], [0.9,0.3,0.5,0.75])
+    assert round(loss,2) == 0.36
+
+    loss = cross_entropy_loss([1,0,0,1,1,0,1,1], [0.9,0.3,0.5,0.75,0.85,0.14,0.93,0.79])
+    assert round(loss,2) == 0.26
+
 
 def test_rms_error():
     assert rms_error([2, 2], [2, 2]) == 0