Compute the gradient for regularized logistic regression

ex2/costFunctionReg.m

@@ -20,6 +20,10 @@ grad = zeros(size(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);
 
+regularization_term = ...
+  lambda/m * (theta .* prepad(ones(length(theta)-1, 1), length(theta), 0));
+grad = 1/m * X' * (sigmoid(X*theta) - y) + regularization_term;
+
 % =============================================================
 
 end