Week 3 Assignments/Logistic Regression and Regularization/mlclass-ex2/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));

% ====================== YOUR CODE HERE ======================
% Instructions: Compute the cost of a particular choice of theta.
%               You should set J to the cost.
%               Compute the partial derivatives and set grad to the partial
%               derivatives of the cost w.r.t. each parameter in theta
%
% Note: grad should have the same dimensions as theta
%


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

grad = (1 / m) * sum( X .* repmat((sigmoid(X*theta) - y), 1, size(X,2)) );





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

end
