title: Subscript indices must be real positive integers or logicals
body: <pre><code>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.
  %
  
      hypothesis = x*theta;
      theta_0 = theta(1) - alpha(1/m)*sum((hypothesis-y)*x);
      theta_1 = theta(2) - alpha(1/m)*sum((hypothesis-y)*x);
      theta(1) = theta_0;
      theta(2) = theta_1;
  
  
  
  
  
  
  
  
  % ============================================================
  
  % Save the cost J in every iteration    
      J_history(iter) = computeCost(X, y, theta);
  
  end
  
  end
  </code></pre>
  
  <p>I keep getting this error </p>
  
  <pre><code>error: gradientDescent: subscript indices must be either positive integers less than 2^31 or logicals
  </code></pre>
  
  <p>on this line right in-between the first theta and =</p>
  
  <pre><code>theta_0 = theta(1) - alpha(1/m)*sum((hypothesis-y)*x);
  </code></pre>
  
  <p>I'm very new to octave so please go easy on me, and
  thank you in advance.
  This is from the coursera course on Machine Learning from Week 2</p>