Other methods which do not fall easily into the above two classes include most notably the extremely powerful scaling method of Vergini and Saraceno, which combines the best elements from both classes (see history below), and is the subject of the next chapter. Also deserving mention are 1) time-propagation (by e.g. split-operator FFT method[18]) followed by extraction of Fourier coefficients, 2) physical simulation by microwave[185,123,93] or acoustic [69] cavities, or even by soap bubble films [6], 3) an interestingly bizarre but impractical recent suggestion by Bulgac [39].