Figure 4.

Adaptation quality measures of the adaptive frequency Hopf oscillator in the (f₀, f_ext) frequency space for different values of the coupling strength ϵ and the learning rate η. For every given (ϵ, η)-parameter pair, from left to right, the relative convergence time $\tilde{\Delta }$, the relative final frequency offset $\tilde{\delta }$, the final relative frequency fluctuation $\tilde{\sigma }$, and the combined quality measure Q are shown in the plane spanned by the initial intrinsic frequency f₀ and the frequency of the external unit sine-wave signal f_ext. As the convergence time is defined as the time difference between the onset of the external signal and the last point of time of more than 5% deviation of the intrinsic frequency from the final average, for high values of $\tilde{\sigma }$, the convergence time cannot be reasonably determined, i.e., takes very high values. For the same reason, even on the diagonal f₀ = f_ext, high convergence times are measured for low values of f_ext.