Linear regression cost function and optimizer in tensorflow

cost_optimizer.py

def get_cost_optimizer_tensor(Y, model, size, learning_rate):
  """
  Tensor for calculating the cost function and the the optimizer for 
  minimizing the cost.
  """
  # Cost function tensor.
  cost_function = tf.reduce_sum(tf.pow(model - Y, 2))/(2 * size) 
  # gradient descent tensor.
  gradient_descent = tf.train.GradientDescentOptimizer(learning_rate) 
  # optimization tensor.
  optimizer = gradient_descent.minimize(cost_function)
  
  return optimizer, cost_function