The two most important cases in application are the almost trivial one in which all the oscillators are identical and the much more interesting one when the parameters of the oscillators are scattered either in frequency or in damping. The consideration of the behavior of an ensemble of identical noninteracting oscillators is the main subject of the classical theory of the dispersion of light. Heterogeneous oscillators must be considered, for example, in the analysis of the scattering of electromagnetic radiation in heated gases, in which the spread of molecular velocities results in Doppler shifts in the radiation’s frequencies with respect to the frequency of the field.