def _smooth_the_residuals(self):
for primary_smooth in self._primary_smooths:<EOL><INDENT>smooth = smoother.perform_smooth(self.x,<EOL>primary_smooth.cross_validated_residual,<EOL>MID_SPAN)<EOL>self._residual_smooths.append(smooth.smooth_result)<EOL><DEDENT>
Apply the MID_SPAN to the residuals of the primary smooths.

"For stability reasons, it turns out to be a little better to smooth
|r_{i}(J)| against xi" - [1]