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First published on Wednesday, Jun 24, 2026 and last modified on Thursday, Jun 25, 2026 by François Chaplais.

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Stability of Slow-Fast Nonlinear Dynamics: Non-Periodic Case

G. Q. Bao Tran Coordinated Science Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA Email

Daniel Liberzon Coordinated Science Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA Email

Hyungbo Shim ASRI, Department of Electrical and Computer Engineering, Seoul National University, Seoul, South Korea Email

Keywords: Nonlinear systems, switched systems, averaging theory, perturbation theory

Abstract

1 Introduction

2 Main Result

3 Proof of Theorem 1

\[ \begin{align*} &\dot{y}(t) = \left(I - \varepsilon \frac{\partial w}{\partial x}(x(t),u_s(t),t/\varepsilon,\varepsilon)\right)\dot{x}(t) \\ &{}- \varepsilon \frac{\partial w}{\partial u_s}(x(t),u_s(t),t/\varepsilon,\varepsilon)\dot{u}_s(t) - \varepsilon \frac{\partial w}{\partial \tau}(x(t),u_s(t),t/\varepsilon,\varepsilon)\frac{1}{\varepsilon}\\ & = f(x(t),u_s(t),u_f(t/\varepsilon)) - \varepsilon \frac{\partial w}{\partial x}(x(t),u_s(t),t/\varepsilon,\varepsilon)\\ &~{}\times f(x(t),u_s(t),u_f(t/\varepsilon))- \varepsilon \frac{\partial w}{\partial u_s}(x(t),u_s(t),t/\varepsilon,\varepsilon)\dot{u}_s(t)\\ &~{} - h(x(t),u_s(t),u_f(t/\varepsilon)) + \varepsilon w(x(t),u_s(t),t/\varepsilon,\varepsilon)\\ & = f_{\text{av}}(y(t),u_s(t)) + f_{\text{av}}(x(t),u_s(t)) - f_{\text{av}}(y(t),u_s(t)) \\ &~{}- \varepsilon \frac{\partial w}{\partial x}(x(t),u_s(t),t/\varepsilon,\varepsilon)f(x(t),u_s(t),u_f(t/\varepsilon)) \\ &~{}- \varepsilon \frac{\partial w}{\partial u_s}(x(t),u_s(t),t/\varepsilon,\varepsilon)\dot{u}_s(t) + \varepsilon w(x(t),u_s(t),t/\varepsilon,\varepsilon). \end{align*} \]
\[ f_{\text{av}}(x(t),u_s(t)) - f_{\text{av}}(y(t),u_s(t)) = \varepsilon F(\Phi_{t,\varepsilon}^{-1}(y(t)),y(t),u_s(t))w(\Phi_{t,\varepsilon}^{-1}(y(t)),u_s(t),t/\varepsilon,\varepsilon), \]
\[ F(x,y,u_s) := \int_0^1 \frac{\partial f_{\text{av}}}{\partial x}(\theta x + (1-\theta)y,u_s)d\theta. \]
\[ \begin{align*} y(t^+) &= \Phi_{t^+,\varepsilon}(x(t^+))= \Phi_{t^+,\varepsilon}(x(t^-)) \\ & = \Phi_{t^+,\varepsilon} (\Phi_{t^-,\varepsilon}^{-1}(y(t^-))). \end{align*} \]
\[ y(t^+) - y(t^-)= -\varepsilon (w(x(t^-),u_s(t^+),t/\varepsilon,\varepsilon) - w(x(t^-),u_s(t^-),t/\varepsilon,\varepsilon)). \]
\[ \begin{align*} &w(x(t^-),u_s(t^+),t/\varepsilon,\varepsilon) - w(x(t^-),u_s(t^-),t/\varepsilon,\varepsilon)\\ &= \int_0^1 \frac{d}{dr} w(x(t^-),\kappa(r),t/\varepsilon,\varepsilon)dr\\ &= \int_0^1 \frac{\partial w}{\partial u_s}(x(t^-),\kappa(r),t/\varepsilon,\varepsilon)(u_s(t^+) - u_s(t^-))dr\\ &= \left(\int_0^1 \frac{\partial w}{\partial u_s}(x(t^-),\kappa(r),t/\varepsilon,\varepsilon)dr\right) (u_s(t^+) - u_s(t^-)). \end{align*} \]
\[ \begin{align*} &\dot{V}(y(t),u_s(t)) = \frac{\partial V}{\partial y}(y(t),u_s(t))(f_{\text{av}}(y(t),u_s(t)) \\ &~~{}+ g_0(y(t),u_s(t),t,\varepsilon)\dot{u}_s(t) \\ &~~{} + g_1(y(t),u_s(t),t,\varepsilon)) + \frac{\partial V}{\partial u_s}(y(t),u_s(t))\dot{u}_s(t). \end{align*} \]
\[ \begin{align*} &\dot{V}(y(t),u_s(t))\leq -c_3 |y(t)|^2 + c_5\delta_1\gamma(\varepsilon)|y(t)|^2\\ &~~ {} + c_4 |y(t)|^2|\dot{u}_s(t)|+ c_5\delta_2 \gamma(\varepsilon)|y(t)|^2|\dot{u}_s(t)| \\ &\leq \left(-\frac{c_3}{c_2} + \frac{c_5}{c_1} \delta_1 \gamma(\varepsilon) +\left(\frac{c_4}{c_1} + \frac{c_5}{c_1} \delta_2 \gamma(\varepsilon)\right)|\dot{u}_s(t)|\right) \\ &~~{}\times V(y(t),u_s(t)). \end{align*} \]
\[ V(y(t^+),u_s(t^+)) - V(y(t^-),u_s(t^+)) \leq (\ell_2 (\gamma(\varepsilon))^2 + \ell_1 \gamma(\varepsilon))|u_s(t^+) - u_s(t^-)|V(y(t^-),u_s(t^-)). \]
\[ \begin{align*} &V(y(t^-),u_s(t^+)) - V(y(t^-),u_s(t^-))\\ &\leq \left|\frac{\partial V}{\partial u_s}(y(t^-), \overline{u}_s)\right||u_s(t^+) - u_s(t^-)|\\ &\leq c_4|y(t^-)||u_s(t^+) - u_s(t^-)|\\ &\leq \ell_0|u_s(t^+) - u_s(t^-)|V(y(t^-),u_s(t^-)), \end{align*} \]
\[ \begin{align*} V(t_2) &\leq \exp\bigg(\left(-\frac{c_3}{c_2} + \frac{c_5}{c_1} \delta_1 \gamma(\varepsilon)\right)(t_2 - t_1)\\ &~{}+\left(\frac{c_4}{c_1} + \ell_2 (\gamma(\varepsilon))^2 + \frac{c_5}{c_1} \max\{\delta_2,1\} \gamma(\varepsilon)\right)\\ &~{} \times\int_{t_1}^{t_2}\|du_s\|\bigg)V(t_1)\\ & \leq \exp\bigg(\left(-\frac{c_3}{c_2} + \frac{c_5}{c_1} \delta_1 \gamma(\varepsilon)\right)(t_2 - t_1)\\ &~ {}+\left(\frac{c_4}{c_1} + \ell_2 (\gamma(\varepsilon))^2 + \frac{c_5}{c_1} \max\{\delta_2,1\} \gamma(\varepsilon)\right)\\ &~{}\times(\mu(t_2 - t_1) + \alpha)\bigg) V(t_1), \end{align*} \]

4 Illustration: Switched System

\[ A_{av,i}^\top P_i + P_i A_{av,i} = -I, ~~ i = 1,2, \]
Figure 1. Unstable state trajectories of system (24) with \( \varepsilon_s = 1\) , \( \varepsilon_f = 0.1\) (left) and \( \varepsilon_s = 4\) , \( \varepsilon_f = 1\) (right).\label{fig1}

5 Conclusion

References

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