docs: def _compute_window_size(self):
          """Determine characteristics of symmetric neighborhood with J/2 values on each side."""
          self._neighbors_on_each_side = int(len(self.x) * self._span) // 2
          self.window_size = self._neighbors_on_each_side * 2 + 1
          if self.window_size <= 1:
              # cannot do averaging with 1 point in window. Force >=2
              self.window_size = 2