```
function [theta, J_history] = gradientDescent(X, y, theta, alpha, num_iters)
%GRADIENTDESCENT Performs gradient descent to learn theta
% theta = GRADIENTDESENT(X, y, theta, alpha, num_iters) updates theta by
% taking num_iters gradient steps with learning rate alpha
% Initialize some useful values
m = length(y); % number of training examples
J_history = zeros(num_iters, 1);
for iter = 1:num_iters
% ====================== YOUR CODE HERE ======================
% Instructions: Perform a single gradient step on the parameter vector
% theta.
%
% Hint: While debugging, it can be useful to print out the values
% of the cost function (computeCost) and gradient here.
%
% For J = 0 and J = 1, which should use the positions of theta 1 and 2 (indexes of octave)
% theta1 - alpha * 1/m * sum( theta0 * x(i) - y(i) ) for all i
% theta2 - alpha * 1/m * sum( theta1 * x(i) - y(i) ) * x(i) for all i
% defining the derivate of theta 1 portion
derivative1 = (1/m)*sum((X*theta) -y);
%Define the complete Equation for theta 1
temp1 = theta(1) - (alpha*derivative1);
% defining the derivate of theta 2 portion
derivative2 = (1/m)*sum(((X*theta) -y).* X(:,2));
%Define the complete Equation for theta 2
temp2 = theta(2) - (alpha*derivative2);
%Derive theta
theta = [temp1;temp2];
% In order to debug, the cost shows the decrease during the iterations.
% jCost = computeCost(X, y, theta)
%disp(jCost)
% ============================================================
% Save the cost J in every iteration
J_history(iter) = computeCost(X, y, theta);
%disp(J_history);
end
end
```

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