# “I sing well-tempered”

## The Ising Model

This explorable illustrates one of the most famous models in statistical mechanics: * The Ising Model*. The model is structurally very simple and captures the properties and dynamics of magnetic materials, such as

*ferromagnets*. It is so general that it is also used to describe opinion dynamics in populations and collective behavior in animal groups.

# “Anomalous Itinerary”

## Lévy flights

This explorable illustrates the properties of a class of random walks known as Lévy flights.
To get the most out of this explorable, you may want to check out the explorable **Albert & Carl Friedrich** on ordinary random walks and diffusion first.

# “Hopfed Turingles”

## Pattern Formation in a simple reaction-diffusion system

With this explorable you can discover a variety of spatio-temporal patterns that can be generated with a very famous and simple autocatalytic reaction diffusion system known as the **Gray-Scott model**. In the model two substances \(U\) and \(V\) interact and diffuse in a two-dimensional container. Although only two types of simple reactions occur, the system generates a wealth of different stable and dynamic spatio-temporal patterns depending on system parameters.

# “Albert & Carl Friedrich”

## Random Walks & Diffusion

This explorable illustrates the geometric and dynamic properties of the physical process of **diffusion** and its intimate relation to a mathematical object known as a **random walk**. It also illustrates graphically the implications of the **central limit theorem** that explains why we so often (* normally*) observe

**Gaussian distributions**in nature. In the context of random walks this means that in the long run and from a great distance the paths of different types of walks become statistically indistiguishable.

# “Critically Inflammatory”

## A forrest fire model

This explorable illustrates, as a representative of a broad range of dynamic phenomena,
a simple model for the spatial spread of forest fires and the dynamic patterns they generate. In the model
two antagonistic processes interplay, the * reproductive growth of vegetation* that continously covers the landscape with trees susceptible to fires and

*that spread across areas of dense vegetation.*

**spontaneously seeded (lightning strikes) forest fires**# “Dr. Fibryll & Mr. Glyde”

## Pulse-coupled oscillators

This explorable illustrates pattern formation in excitable media. The example explored here
in a system of **pulse-coupled oscillators** that are arranged on a two-dimensional lattice and interact with their neighbors by delivering excitatory pulses to them and receiving them in return. This model is sometimes used to study synchronization and can capture the dynamics of activation in layers of neurons as well as the spatial patterns of signaling molecules that play a role in microbial aggregation processes.

# “Stranger Things”

## Strange attractors

This explorable illustrates the structure and beauty of * strange attractors* of two-dimensional discrete maps. These maps generate sequences of pairs of number \((x_n,y_n)\) where the index \(n=0,1,2,...\) denotes the step of the iteration process that starts at the point \((x_0,y_0)\). The map is defined by two functions \(f(x,y)\) and \(g(x,y)\) that determine the point \((x_{n+1},y_{n+1})\) given \((x_{n},y_{n})\):

# “Kelp!!!”

## A stochastic cellular automaton

This explorable illustrates how fractal growth patterns can be generated by **stochastic cellular automata**. Cellular automata are spatially and temporally discrete dynamical systems that are conceptually very straightforward but can generate unexpected complex behavior, often fractal-like structures reminiscent of patterns we see in natural systems.

# “Knitworks”

## Growing complex networks

This explorable illustrates network growth based on * preferential attachment*, a variant of the

**Barabasi-Albert model**that was introduced to capture strong heterogeneities observed in many natural and technological networks. It has become a popular model for scale-free networks in nature.

Preferential attachment means that nodes that enter the network during a growth process preferentially connect to nodes with specific properties. In the original system, they preferentially connect to existing nodes that are already well connected, increasing their connectivity even further. This *rich get richer* effect generates networks in which a few nodes are very strongly connected and very many nodes poorly.

# “If you ask your XY”

## The XY model of statistical mechanics

This explorable illustrates pattern formation and dynamics in the **\(XY\)-model**, an important model in statistical mechanics for studying phase-transitions and other phenomena. It's a generalization of the famous **Ising-Model**. The \(XY\)-model is actually quite simple.

# “Ride my Kuramotocycle!”

## The Kuramoto model

This explorable illustrates the ** Kuramoto model** for phase coupled oscillators. This model is used to describe synchronization phenomena in natural systems, e.g. the flash synchronization of fire flies or wall-mounted clocks.

# “Barista's Secret”

## Percolation on a lattice

This explorable illustrates a process known as percolation. ** Percolation** is a topic very important for understanding processes in physics, biology, geology, hydrology, horstology, epidemiology, and other fields.

**is the mathematical tool designed for understanding these processes.**

*Percolation theory*# “Double Trouble”

## The double pendulum

This explorable illustrates the beautiful dynamical features of the **double pendulum**, a famous idealized nonlinear mechanical system that exhibits deterministic chaos.
The double pendulum is essentially two simple pendula joined by a bearing. It's a classic complex system in which a simple setup generates rich and seemingly unpredictable behavior. The only force that is acting on it is gravity. There's no friction.

# “Particularly Stuck”

## Diffusion Limited Aggregation

This explorable illustrates a process known as diffusion-limited aggregation (DLA). It's a kinetic process driven by randomly diffusing particles that gives rise to fractal structures, reminiscent of things we see in natural systems. The process has been investigated in a number of scientific studies, e.g. the seminal paper by Witten & Sander.

# “Cycledelic”

## The spatial rock-paper-scissors game

This explorable of a pattern forming system is derived from a model that was designed to understand co-existance of cyclicly interacting species in a spatially extended model ecosystem. Despite its simplicity, it can generate a rich set of complex spatio-temporal patterns depending on the choice of parameters and initial conditions.

# “Kick it like Chirikov”

## The kicked rotator (standard map)

In this explorable you can investigate the dynamics of a famous two-dimensional, time discrete map, known as the standard or Chirikov–Taylor map, one of the most famous simple systems that exhibits determinstic chaos.

# “Keith Haring's Mexican Hat”

## Pattern Formation by Local Excitation and Long-Range Inhibition

This explorable illustrates one of the most basic pattern forming mechanism: Local excitation and long range inhibition. This mechanism or similar ones are responsible for patterns observed in neural tissue, animal fur and spatial heterogeneity in social systems.

# “Spin Wheels”

## Phase-coupled oscillators on a lattice

This explorable illustrates some interesting and beautiful properties of oscillators that are spatially arranged on a lattice and interact with their neighbors.