def _remove_observation_from_variances(self, xj, yj):
term1 = self.window_size / (self.window_size - <NUM_LIT:1.0>) * (xj - self._mean_x_in_window)<EOL>self._covariance_in_window -= term1 * (yj - self._mean_y_in_window)<EOL>self._variance_in_window -= term1 * (xj - self._mean_x_in_window)<EOL>
Quickly update the variance and co-variance for the deletion of one observation.