Autonomous dynamical system

Oct 13, 2025 by pynkocean.com 51 views

Can we construct a autonomous dynamical system with an attractive singleton at which the system is not Lyapunov (asymptotically) stable?

In the realm of dynamical systems, the concepts of attraction and stability are often intertwined, but they do not necessarily prove each other. A system can be attractive, yet unstable, or stable, yet repulsive. In this article, we will delve into the possibility of constructing an autonomous dynamical system with an attractive singleton, but not Lyapunov (asymptotically) stable.

To begin with, let's define the key concepts involved:

Autonomous dynamical system: A system described by a differential equation of the form $\frac{dx}{dt} = f(x(t))$ , where $x(t)$ is the state of the system at time $t$ , and $f$ is a function that determines the evolution of the system.
Attractive singleton: A point in the state space that attracts all other points, meaning that the system converges to this point as time approaches infinity.
Lyapunov stability: A system is Lyapunov stable if it remains bounded in a neighborhood of an equilibrium point, even if the initial conditions are perturbed.

The question at hand is whether it is possible to construct an autonomous dynamical system with an attractive singleton, but not Lyapunov (asymptotically) stable. In other words, can we design a system that converges to a single point, but does not remain bounded in a neighborhood of that point?

To address this question, let's consider a simple example. Consider the system:

\frac{dx}{dt} = -x^3

This system has a single equilibrium point at $x=0$ , which is attractive. However, the system is not Lyapunov stable, because the function $V(x) = x^2$ is a Lyapunov function for the system, and its derivative along the trajectories of the system is:

\frac{dV}{dt} = -2x^4

which is negative definite, but not bounded in a neighborhood of the equilibrium point.

The previous example is a special case, and we can generalize it to a larger class of systems. Consider the system:

\frac{dx}{dt} = -x^p

where $p$ is a positive integer. This system has a single equilibrium point at $x=0$ , which is attractive. However, the system is not Lyapunov stable, because the function $V(x) = x^{p+1}$ is a Lyapunov function for the system, and its derivative along the trajectories of the system is:

\frac{dV}{dt} = -(p+1)x^{2p+1}

which is negative definite, but not bounded in a neighborhood of the equilibrium point.

In conclusion, we have shown that it is possible to construct an autonomous dynamical system with an attractive singleton, but not Lyapunov (asymptotically) stable. This result highlights the importance of distinguishing between attraction and stability in dynamical systems.

The implications of this result are far-reaching, and have significant consequences for the analysis and design of dynamical systems. For example, in control theory, the stability of a system is a crucial property that determines its behavior. However, the result presented here shows that stability is not the only property that matters, and that attraction can be a more important property in certain contexts.

There are many open questions and directions for future research in this area. For example, can we generalize the result presented here to more general classes of systems? Can we find conditions under which a system is both attractive and Lyapunov stable? These are just a few of the many questions that remain to be answered.

[1] Lyapunov, A. M. (1892). The general problem of the stability of motion. International Journal of Control, 55(3), 531-534.
[2] LaSalle, J. P. (1976). The stability of dynamical systems. Regional Conference Series in Applied Mathematics, 25.
[3] Khalil, H. K. (2002). Nonlinear systems. Prentice Hall.

The following is a list of theorems and lemmas used in this article:

Theorem 1: If a system has a Lyapunov function, then it is Lyapunov stable.
Theorem 2: If a system is Lyapunov stable, then it is attractive.
Lemma 1: If a system has a Lyapunov function, then its derivative along the trajectories of the system is negative definite.

Note: The theorems and lemmas listed above are not proven in this article, but can be found in the references listed above.
Q&A: Can we construct a autonomous dynamical system with an attractive singleton at which the system is not Lyapunov (asymptotically) stable?

Q: What is the difference between attraction and stability in dynamical systems? A: Attraction refers to the property of a system to converge to a single point or a set of points, while stability refers to the property of a system to remain bounded in a neighborhood of an equilibrium point.

Q: Can a system be attractive but not stable? A: Yes, it is possible to construct a system that is attractive but not stable. For example, consider the system $\frac{dx}{dt} = -x^3$ . This system has a single equilibrium point at $x=0$ , which is attractive, but the system is not Lyapunov stable.

Q: Can a system be stable but not attractive? A: Yes, it is possible to construct a system that is stable but not attractive. For example, consider the system $\frac{dx}{dt} = -x$ . This system has a single equilibrium point at $x=0$ , which is stable, but the system is not attractive.

Q: What is the significance of Lyapunov stability in dynamical systems? A: Lyapunov stability is a crucial property in dynamical systems, as it ensures that the system remains bounded in a neighborhood of an equilibrium point. This property is essential in control theory, as it determines the behavior of a system.

Q: Can we generalize the result presented in this article to more general classes of systems? A: Yes, it is possible to generalize the result presented in this article to more general classes of systems. For example, consider the system $\frac{dx}{dt} = -x^p$ , where $p$ is a positive integer. This system has a single equilibrium point at $x=0$ , which is attractive, but the system is not Lyapunov stable.

Q: Can we find conditions under which a system is both attractive and Lyapunov stable? A: Yes, it is possible to find conditions under which a system is both attractive and Lyapunov stable. For example, consider the system $\frac{dx}{dt} = -x$ . This system has a single equilibrium point at $x=0$ , which is both attractive and Lyapunov stable.

Q: What are the implications of this result for control theory? A: The result presented in this article has significant implications for control theory, as it highlights the importance of distinguishing between attraction and stability in dynamical systems. This result can be used to design more effective control systems that take into account both attraction and stability.

Q: What are the open questions and directions for future research in this area? A: There are many open questions and directions for future research in this area. For example, can we generalize the result presented in this article to more general classes of systems? Can we find conditions under which a system is both attractive and Lyapunov stable? These are just a few of the many questions that remain to be answered.

Q: What are the references used in this article? A: The references used in this article are:

[1] Lyapunov, A. M. (1892). The general problem of the stability of motion. International Journal of Control, 55(3), 531-534.
[2] LaSalle, J. P. (1976). The stability of dynamical systems. Regional Conference Series in Applied Mathematics, 25.
[3] Khalil, H. K. (2002). Nonlinear systems. Prentice Hall.

Q: What is the appendix of this article? A: The appendix of this article is a list of theorems and lemmas used in this article. The theorems and lemmas listed above are not proven in this article, but can be found in the references listed above.