costFunction <- function(theta, X, y){
  
  #   Compute cost and gradient for logistic regression
  #
  #   J <- costFunction(theta, X, y) computes the cost for logistic regression,
  #   using theta parameters

  # Initialize some useful values
  m <- length(y) # number of training examples
  
  # ====================== YOUR CODE HERE ======================
  # Instructions: Compute the cost of a particular choice of theta.
  #               You should set J to the cost.
 
  
  
  # ============================================================
  
  return(J)
}