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
Determine characteristics of symmetric neighborhood with J/2 values on each side.