Maximal propagation distance of the effect of some disturbance within a net (after K. WILSON, 1989, p.92).
This maximal distance plays an important role in composite systems, as it commands the percolation phenomena.
WILSON observes that: "Regions separated by a distance superior to the correlation length are independent" (Ibid).
The correlation length is variable according to the state of the system. It is major in strongly connected systems and less so in weakly connected ones.
This is verified for example in the disappearance of magnetization at some distinct temperature (CURIE's temperature) (Ibid), or in the spontaneous extinction of a forest fire inside of the already burnt down zone or, again, in the extinction of a pandemy when the number of victims exceeds some defined limit.
WILSON points out that: "That which is most significant when the correlation length increases is that the small variations do not disappear when variations of a greater size expand: they merely become a finer structure, superposed to the larger scale structure" (Ibid).
As a result, systems of this type show a fractal structure and may manifest local behaviors at variance with the global one.
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Bertalanffy Center for the Study of Systems Science (2020). Title of the entry. In Charles François (Ed.), International Encyclopedia of Systems and Cybernetics (2). Retrieved from www.systemspedia.org/[full/url]
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