Difference between state variables of the two rival models (states of Model 1 minus states of Model 2) in the Input design for model discrimination case. Simulation results for Models 1 and 2 with a constant (a), sine (b), or square wave (c) perturbation of the basal input S0 until time 60 (the inputs in Figure 4). The output variable (on which the choice of the optimal frequency depends) is R* and ||u||2 = 1. The corresponding ||y1 - y2||2 values are 0.0070, 0.0195, and 0.0182, respectively. Note that the input signal S0 + u is not included in the figure.