Describes perfect lossless waves on the surface of a string, or on a water surface.

JavaScript toy solvers:

- https://jtiscione.github.io/webassembly-wave/index.html circular domain, create waves with mouse click
- https://dionyziz.com/graphics/wave-experiment/ with useless 3D WebGL visualization :-), waves with mouse click. Solving itself done on CPU, not GPU.

As mentioned at: https://math.stackexchange.com/questions/579453/real-world-application-of-fourier-series/3729366#3729366 from solving partial differential equations with the Fourier series citing https://courses.maths.ox.ac.uk/node/view_material/1720, analogously to the heat equation, the wave linear equation can be be solved nicely with separation of variables.