Removed unused cost function

Author: mnielsen

code/network_basic.py

@@ -119,17 +119,12 @@ def evaluate(self, test_data):
                         for (x, y) in test_data]
         return sum(int(x == y) for (x, y) in test_results)
 
-    def cost(self, x, y):
-        """Return the quadratic cost associated to the network, with
-        input ``x`` and desired output ``y``.  Note that there is no
-        regularization."""
-        return np.sum((self.feedforward(x)-y)**2)/2.0
-
     def cost_derivative(self, output_activations, y):
         """Return the vector of partial derivatives \partial C_x /
-        \partial a for the output activations, ``a``.  For the
-        unregularized quadratic cost this is just the difference
-        between the output activations and the desired output, ``y``."""
+        \partial a for the ``output_activations``.  For the
+        (unregularized) quadratic cost this is just the difference
+        between the ``output_activations`` and the desired output, 
+        ``y``."""
         return (output_activations-y) 
 
 #### Miscellaneous functions