costFunction.m

function [J, grad] = costFunction(theta, X, y)
%COSTFUNCTION Compute cost and gradient for logistic regression
%   J = COSTFUNCTION(theta, X, y) computes the cost of using theta as the
%   parameter for logistic regression and the gradient of the cost
%   w.r.t. to the parameters.

% Initialize some useful values
m = length(y); % number of training examples

% You need to return the following variables correctly
J = 0;
grad = zeros(size(theta));


h = sigmoid(X*theta);
J = ((-y)'*log(h)-(1-y)'*log(1-h))/m;

% calculate grads
grad = (X'*(h - y))/m;

% =============================================================

end