Overview
The term Variety was introduced by W. Ross Ashby to denote the count of the total number of states of a system. The condition for dynamic stability under perturbation (or input) was described by his Law of Requisite Variety. Ashby says:
Thus, if the order of occurrence is ignored, the set
c, b, c, a, c, c, a, b, c, b, b, a
which contains twelve elements, contains only three distinct elements- a, b, c. Such a set will be said to have a variety of three elements.
He adds
The observer and his powers of discrimination may have to be specified if the variety is to be well defined.
Variety can be stated as an integer, as above, or as the logarithm to the base 2 of the number i.e. in bits.
Read more about this topic: Variety (cybernetics)