“…The study in [5] has since been extended to more general references [6], [7], and discrete-time systems [18]. There have also been generalizations to nonright-invertible plant [20], [3], to the cases where the controller has previewed information of [7], where the plant input is subject to saturation [12], and where the tracking performance measure includes the input energy [4], respectively. It has been shown that, consistent with common intuitions, the preview of the reference can reduce the best achievable tracking error and on the other hand any input saturation or any input energy constraint would likely increase the best achievable tracking error.…”