# Partial control of chaos: how to avoid undesirable behaviors with small controls in presence of noise

## TL;DR

This paper reviews the partial control method that uses minimal control to prevent undesirable transient chaos in noisy dynamical systems by maintaining trajectories within a safe set.

## Contribution

It provides a comprehensive survey of the partial control method, its variations, and applications across diverse dynamical systems, demonstrating its effectiveness in controlling chaos with small controls.

## Key findings

- Control can be achieved with control inputs smaller than noise levels.
- The safe set concept effectively sustains transient chaos.
- Partial control is versatile across different system dimensions.

## Abstract

The presence of a nonattractive chaotic set, also called chaotic saddle, in phase space implies the appearance of a finite time kind of chaos that is known as transient chaos. For a given dynamical system in a certain region of phase space with transient chaos, trajectories eventually abandon the chaotic region escaping to an external attractor, if no external intervention is done on the system. In some situations, this attractor may involve an undesirable behavior, so the application of a control in the system is necessary to avoid it. Both, the nonattractive nature of transient chaos and eventually the presence of noise may hinder this task. Recently, a new method to control chaos called \emph{partial control} has been developed. The method is based on the existence of a set, called the safe set, that allows to sustain transient chaos by only using a small amount of control. The surprising result is that the trajectories can be controlled by using an amount of control smaller than the amount of noise affecting it. We present here a broad survey of results of this control method applied to a wide variety of dynamical systems. We also review here all the variations of the partial control method that have been developed so far. In all the cases various systems of different dimensionality are treated in order to see the potential of this method. We believe that this method is a step forward in controlling chaos in presence of disturbances.