Add cost function for regularized logistic regression

ex2/costFunctionReg.m

@@ -17,10 +17,8 @@ grad = zeros(size(theta));
 %               Compute the partial derivatives and set grad to the partial
 %               derivatives of the cost w.r.t. each parameter in theta
 
-
-
-
-
+J = 1/m * (-y'*log(sigmoid(X*theta)) - (1-y)'*log(1-sigmoid(X*theta))) ...
+    + lambda/(2*m) * theta(2:end)' * theta(2:end);
 
 % =============================================================