Variety (cybernetics)
In operations research.
Overview
The term "variety" was presents by W. Ross Ashby to come on his analysis of machines to their variety of possible behaviors.: 121 Ashby says:: 126
The word variety, in description to a manner of distinguishable elements, will be used to mean either i a number of distinct elements, or ii a logarithm to the base 2 of the number, the context indicating the sense used.
In thecase, variety is measured in sequence or multiset is the number of distinct symbols in it. For example, the sequence has a variety of four. As a degree of uncertainty, variety is directly related to information: .: 26
has a variety of four. As a degree of uncertainty, variety is directly related to information: 
.: 26 Since the number of distinguishable elements depends on both the observer and the set, "the observer as well as his powers of discrimination may develope to be subjected if the variety is to be alive defined".: 125 Gordon Pask distinguished between the variety of the chosen acknowledgment frame and the variety of the system the observer builds up within the acknowledgment frame. The reference frame consists of a state space and the set of measurements usable to the observer, which do total variety , where is the number of states in the state space. The system the observer builds up begins with the full variety , which is reduced as the observer loses uncertainty approximately the state by learning to predict the system. if the observer can perceive the system as a deterministic machine in the assumption reference frame, observation may reduce the variety to zero as the machine becomes totally predictable.: 27
, where 
is the number of states in the state space. The system the observer builds up begins with the full variety Laws of nature constrain the variety of phenomena by disallowingbehavior.: 130 Ashby submission two observations he considered laws of nature, the law of experience and the law of requisite variety. The law of experience holds that machines under input tend to lose information about their original state, and the law of requisite variety states a necessary, though not sufficient, given for a regulator to exert anticipatory leadership by responding to its current input rather than the preceding output as in error-controlled regulation.