PPT Slide
Consider examples of patterns discussed before and notice that all of them can be described in terms of some quantity y which depends on space and time. The spatial dependence of y describes the structure of the pattern whereas the time dependence of y tells us how the pattern evolves. A natural way of defining y for a stationary pattern is to measure the “size” of the pattern with respect to some average value. For instance, periodic oscillations will be described as an alternation between positive and negative values of y. With this convention, the absence of a pattern corresponds to y =0.