Скачать или смотреть Sunset at Research Triangle Park

The angles of the triangle used here are 90°, 60° and 30°, making it half an equilateral triangle, that can be used to pave the plane. Therefore the dynamics of the billiard in this domain is regular, because the evolution of a circular wave front can be obtained by taking a circle of growing radius, and folding it back into the original triangle. This is similar to the case of the square in the video    • Low sea in the square with diamonds  

Music: "Mia", by Jeremy Blake‪@RedMeansRecording‬

The simulation solves the wave equation with a little bit of "elasticity" (a harmonic restoring force). The algorithm is adapted from this paper: https://hplgit.github.io/fdm-book/doc...

C code: https://www.idpoisson.fr/berglund/vid... (some parameters have to be adapted).
Why don't some of you try some other billiard shapes, parameter values and colors, and post the results on YouTube?

You may be interested in some science outreach articles: https://images.math.cnrs.fr/_Berglund...