[Physicist]

Orthogonal functions are used throughout physics. The most elementary set is sines and cosines, but there are many more, and each has a different use. Bessel functions, for example, are very useful in describing things that have a cylindrical symmetry.

[gjenkins]

I just spent a semester studying and using the fourier transform, and I am still far from being comortable with it. Unfortunately, I really wanted to get to wavelets.