This paper presents techniques for evaluating control algorithms. Transfer functions that characterize the filtering effects of the control forces, control force effects, and response effects of control algorithms are also introduced. The control efficiency of representative control algorithms is illustrated using unified criterion indexes defined by transfer functions. We then present a new sub-optimal control algorithm that can be obtained by combining information on the causality of the impulse response functions and wave propagation phenomena. With reference to the causality of the impulse.response function of the feedforward control force, we discuss the possibility of realizing optimal closed-open-loop control.
