DynamicalBilliards is an easy-to-use, modular and extendable Julia package for dynamical billiards in two dimensions. It is part of JuliaDynamics, an organization dedicated to creating high quality scientific software.

Latest news

The timeseries! function now supports evolving particles until a certain condition (specified by a function) is met.

A dynamical billiard is a system where a particle is propagating inside a domain, bouncing from obstacle to obstacle (i.e. the boundary of the domain) by a specular reflection at the boundary of the obstacles. This basic idea can be extended in many ways, one of which is replacing the particle orbit from a straight line to a circle.

Billiard systems have been used extensively in mathematics, nonlinear dynamics and chaos and played an important role in the development of nonlinear science. The wikipedia page has many examples of different types of billiards. Also, the scholarpedia entry is a good read on the subject.

## Features

• Particles are evolved by solving exactly the geometric equations for intersections between lines, circles, ellipses, and other shapes. There are no approximations done regarding the dynamics.
• Modular creation of a Billiard from well defined obstacles. Arbitrary billiard shapes can be made and no shape is "hard coded".
• Full support for both straight and magnetic propagation of a particle in a billiard table.
• During magnetic propagation the particle orbit is a circle instead of a line!
• All features exist for both types of propagation!
• See the High Level API to get started!
• Support for creating Random initial conditions in an arbitrary billiard.
• Ray-Splitting: a particle may propagate through an obstacle given arbitrary transmission and refraction laws. This is also known as a "semiclassical billiard".
• Poincaré Sections (intersections with arbitrary plane).
• Boundary Maps.
• Escape Times & Mean Collision Times.
• Lyapunov Exponents.
• Support for both coordinate systems: 3D real space and boundary coordinates.
• Novel algorithms that compute the portion of either the 2D boundary space or the 3D real space that an orbit covers as a particle evolves. See the Phase Spaces section.
• Easy to use low-level interface, described at the Internals page.
• Specialized tools for mushroom billiards.
• Full support for Visualizing & Animating billiards and motion in billiards.
• Brutal tests that confirm the package works and overcomes numerical precision issues.

This package does not support finite-sized particles and, as a result, there is also no support for collision between particles.

## Citing

If you have used this package for research that resulted in a publication, please be kind enough to cite the software paper associated with DynamicalBilliards. The DOI is https://doi.org/10.21105/joss.00458 and you can cite as:

G. Datseris, The Journal of Open Source Software 2, 458 (2017).

or if you use BibTeX:

@article{Datseris2017,
doi = {10.21105/joss.00458},
url = {https://doi.org/10.21105/joss.00458},
year  = {2017},
month = {nov},
volume = {2},
number = {19},
pages = {458},
author = {George Datseris},
title = {{DynamicalBilliards}.jl: An easy-to-use,  modular and extendable Julia package for Dynamical Billiard systems in two dimensions.},
journal = {The Journal of Open Source Software}
}

In addition, if you are using the functionality to compute Lyapunov exponents in billiards, then please cite the following Chaos publication:

@article{Datseris2019,
doi = {10.1063/1.5099446},
url = {https://doi.org/10.1063/1.5099446},
year = {2019},
month = sep,
publisher = {{AIP} Publishing},
volume = {29},
number = {9},
pages = {093115},
author = {George Datseris and Lukas Hupe and Ragnar Fleischmann},
title = {Estimating Lyapunov exponents in billiards},
journal = {Chaos: An Interdisciplinary Journal of Nonlinear Science}
}

## Installation

This package is registered, simply use ] to get into the package manager mode and then type add DynamicalBilliards to install it. The stable documentation accompanies the version installed with add.

To confirm the validity of your installation you can run the tests of DynamicalBilliards. This can be done via ] test DynamicalBilliards.

### Plotting

Plotting is done through the PyPlot module. All plotting functions are brought into scope when using PyPlot is done.

In addition, for animations using the function animate_evolution the ffmpeg software must be accessible from the command line.

## How to easily code a Billiard

We have created a Jupyter notebook that showcases how easy it is to simulate a dynamical billiard using Julia. This notebook is an educative example of both using Multiple Dispatch and of how the internal code of DynamicalBilliards works. It also highlights the extendibility of the core code.

Besides a Jupyter notebook, this tutorial is also available as an interactive article in the new platform NextJournal here.

## Support

If you are having any kind of problems with DynamicalBilliards do not hesitate to seek for support! There are numerous ways to do that:

Everyone is welcomed to contribute to DynamicalBilliards! If you have some new algorithm, types of Obstacles or anything new to add, do not hesitate! For formal questions about e.g. structuring of code it is best to contact us through the gitter chatroom or by opening a new Pull Request and asking for a review of your code.