一系列圓，每個圓的圓心在另一個圓上，每個圓都在以某一速率自轉，同時繞着“父親圓”以某一速率公轉，這樣的模型可以無限趨近於任意的複雜模型
The smooth motion of rotating circles can be used to build up any repeating curve even one as angular as a digital square wave. Each circle spins at a multiple of a fundamental frequency, and a method called Fourier analysis shows how to pick the radiuses of the circles to make the picture work. Decomposing signals like this lies at the heart of a lot of signal processing.
