Contents

# Contents

## Idea

A dynamical system is a space $X$ (often a bare set or a manifold) together with a “law of motion” expressed by the action of a monoid $A$:

$A \times X \longrightarrow X \,.$

To model continuous time-evolution one may take $A = (\mathbb{R}, +)$ to be the additive group of real numbers.

For discrete time evolution $A = (\mathbb{Z}, +)$ is the additive group of integers (or just the monoid $(\mathbb{N}, +)$ of natural numbers). In this case the law of motion is often given by an initial value problem for a differential equation “of evolution type”.

In this case, the dynamical system is equivalently a space $X$ equipped with an automorphism (this being the action of the unit element in $\mathbb{Z}$, sometimes called the “shift”).

Sometimes the evolution is only partially defined; this is most often in dynamical systems induced by evolution differential equations which do not necessarily have existence of solutions for arbitrary large time, or the dynamical system is defined only for nonnegative time.

The definition evidently makes sense quite generally internal to various ambient categories: For instance one considers complex dynamics, algebraic dynamics, arithmetic dynamics and so on.

Dynamical systems are used to describe not only physical motions but also the behaviour of parameters of various systems, e.g. in sociological, financial, weather and other models.

## References

### General

• Boris Hasselblatt, Anatole Katok, Handbook of dynamical systems, contents

### Category-theoretic formulations

Discussion of dynamical systems in terms of category theory (see also at categorical systems theory):

Monograph:

Exposition:

• David Jaz Myers, Double Categories of Dynamical Systems (2020) [pdf]

• David Jaz Myers, A general definition of open dynamical systems, talk at MIT Category Theory Seminar (2020) [video:YT]

Last revised on October 25, 2023 at 09:13:00. See the history of this page for a list of all contributions to it.