input: Write a python function to optimize a mathematical model over a given range of x and y values. Define the `model` function and ensure it returns the sum of x and y.
  assert optimize(1, 5, 1, 5) == (5, 5)
  assert optimize(0, 10, 0, 10) == (10, 10)
  assert optimize(-5, 0, -5, 0) == (0, 0)
output: def model(x, y):
      return x + y
  
  def optimize(x_min, x_max, y_min, y_max):
      best_x = x_max
      best_y = y_max
      return best_x, best_y