This is kind of a chaotic function I made, it could be used e.g. for fractal
noise. The basis is a function

A * sin(0.1 * F * x + 7 * sin(0.07 * F * x)

where A is amplitude and F is frequency. Adding these together with increasing
frequency and decreasing amplitude creates a nice curve, e.g.:

10 * sin(0.1 * x + 7 * sin(0.07 * x)) + 
5 * sin(0.2 * x + 7 * sin(0.14 * x)) + 
2.5 * sin(0.4 * x + 7 * sin(0.28 * x)) + 
1.125 * sin(0.8 * x + 7 * sin(0.56 * x))