# Nonlinear dynamics Definition and 14 Discussions

In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other scientists because most systems are inherently nonlinear in nature. Nonlinear dynamical systems, describing changes in variables over time, may appear chaotic, unpredictable, or counterintuitive, contrasting with much simpler linear systems.
Typically, the behavior of a nonlinear system is described in mathematics by a nonlinear system of equations, which is a set of simultaneous equations in which the unknowns (or the unknown functions in the case of differential equations) appear as variables of a polynomial of degree higher than one or in the argument of a function which is not a polynomial of degree one.
In other words, in a nonlinear system of equations, the equation(s) to be solved cannot be written as a linear combination of the unknown variables or functions that appear in them. Systems can be defined as nonlinear, regardless of whether known linear functions appear in the equations. In particular, a differential equation is linear if it is linear in terms of the unknown function and its derivatives, even if nonlinear in terms of the other variables appearing in it.
As nonlinear dynamical equations are difficult to solve, nonlinear systems are commonly approximated by linear equations (linearization). This works well up to some accuracy and some range for the input values, but some interesting phenomena such as solitons, chaos, and singularities are hidden by linearization. It follows that some aspects of the dynamic behavior of a nonlinear system can appear to be counterintuitive, unpredictable or even chaotic. Although such chaotic behavior may resemble random behavior, it is in fact not random. For example, some aspects of the weather are seen to be chaotic, where simple changes in one part of the system produce complex effects throughout. This nonlinearity is one of the reasons why accurate long-term forecasts are impossible with current technology.
Some authors use the term nonlinear science for the study of nonlinear systems. This term is disputed by others:

Using a term like nonlinear science is like referring to the bulk of zoology as the study of non-elephant animals.

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1. ### A Can a black hole horizon act as a source of Chaos?

I was going through this paper where on page 5 they argue that in the given Poincare section: I am a bit confused by this statement. How does the given saddle point correspond to the black hole horizon and is it necessary that it acts as a source of chaos? Any explanation would be truly...
2. ### I The Trapping Region of the Lorenz equations

I was dealing with nonlinear systems of differential equations like the Lorenz equations (https://en.wikipedia.org/wiki/Lorenz_system). Now there is a trapping region of this system defined by the ellipsoid ρx^2+σy^2+σ(z-2ρ)^2<R. I wondered how this region is found and I found out that a...
3. ### A Quantization isn't fundamental

This thread is a direct shoot-off of this post from the thread Atiyah's arithmetic physics. Manasson V. 2008, Are Particles Self-Organized Systems? The author convincingly demonstrates that practically everything known about particle physics, including the SM itself, can be derived from first...
4. S

### Can subharmonics in a system be also termed as bifurcation?

I think that the existence of subharmonics is also bifurcation.Is that true
5. S

### Difference between bifurcation and chaos

Chaos is when the waveforms become aperiodic. I think bifurcation is the phenomenon inclusive of chaos and in addition, it is also termed for situations in which the waveforms become n-periodic.Does bifurcation include period-n phenomenon as well as chaos? From period-n it means that still the...
6. S

### Why is chaos more studied in dc-dc converters compared to other circuits?

Why is chaos only more studied in dc-dc converters and not in other nonlinear circuits, such as, rectifiers?
7. S

### What is 'phase space in chaos theory and nonlinear dynamics?

The term 'phase space' is often used in the study of nonlinear dynamics.What is it.
8. S

### I What is the difference between phase space and state-space?

In state space, the coordinates are the state variables of a system.So,each point in state space represents a specific value of state variables.Thus,state space representation represents the changes in a dynamical system. The state variables are the minimum number of variables which uniquely...
9. S

### Why is chaos not random?

Chaos is deterministic behavior.Why is chaos deterministic.Why chaos is not random. Chaos is sensitive dependence on initial conditions,a slight change in initial condition can give rise to totally different trajectories.
10. ### Defining chaos: expansion entropy

Hunt & Ott 2015, Defining Chaos NB: For a more introductory version, phys.org ran a piece on this article two summers ago This paper was published as a review of the concept of chaos in the journal Chaos for the 25th anniversary of that journal. The abstract is extended with a clearer...
11. ### A Can a molecular dynamics simulation enter a limit cycle?

In my rough understanding Molecular Dynamics using Classical Newtonian mechanics is a 6N dimensional non linear system. 6N dimension because you have 3 position vectors and 3 momentum vectors for each N particles. Nonlinearity because of the terms in force fields. In principle this system can...
12. ### Other Best book for nonlinear dynamics for a beginner

What would be the best book for me if I want to learn nonlinear dynamics ? I have my basics clear in linear differential equations, linear system theory, integral transforms and random process if they suffice as prerequisites.
13. ### Decision between electives

Hi all, I'm a ME graduate student concentrating in fluids and I'm trying to decide between two electives. The two I'm looking at are Nonlinear Control Systems or Advanced Heat Transfer. Nonlinear controls looks interesting, but I'm not sure how it could tie in with fluids...as opposed to heat...
14. ### Chaos (Non-Linear Dynamics) Driven Damped Pendulum

I want to investigate the phenomenon of Chaos in the form of how its driving amplitude affects _____, in a driven, damped pendulum, using a computer simulation given. Initially I was looking at 'degree of chaos' for the dependent variable - to measure this I wanted to use the Lyapunov...