Appendix
We used the parameters setting shown in Table 1 in all the simulations. \(\varDelta t\) denotes the time step width used when we convert continuous-time systems into discrete-time systems. (i.e., the discrete time n corresponds to the continuous time \(n\varDelta t\).)
In Fig. 2, we used the following equation for the periodic teacher signal d(t):
$$\begin{aligned} d(t) = 0.2 \cdot \left[ \sin \left( \frac{2\pi t }{1.0}\right) + \sin \left( \frac{2\pi t}{2.0}\right) + \sin \left( \frac{2\pi t}{4.0}\right) \right] + 1.5. \end{aligned}$$
(23)
In Fig. 3, we used the following equation for the periodic teacher signal d(t):
$$\begin{aligned} d(t) = 0.5 \cdot \left[ \sin \left( \frac{2\pi t}{2.0}\right) \right] + 1.5. \end{aligned}$$
(24)
In Fig. 4, we used the following equation for the periodic teacher signal d(t) with the variable period T:
$$\begin{aligned} d(t) = 0.5 \cdot \left[ \sin \left( \frac{2\pi t}{T}\right) \right] + 1.5, \end{aligned}$$
(25)
and we searched the minimum appropriate \(T_0\) with the interval of 0.1 s.
Table 1. Model parameters common in all the simulations.