In New York, people speak fast. In the American South, they speak slowly. Both of them are a form of politeness, understood in a different way. In New York, you speak quickly because you respect the value of the other person’s time and you don’t want to take up too much of it. In the South, you speak slowly because you want to respect the person by... See more

With Neumann or Neumann-like (e.g. Robin) conditions you want to be careful that you discretize the boundary derivative in a way which has the same order as your discretization of the interior derivatives