Functions as Permutations: Regarding No Free Lunch, Walsh Analysis and Summary Statistics
edited by: Marc Schoenauer, Kalyanmoy Deb, Günther Rudolph, Xin Yao, Evelyne Lutton, JuanJulian Merelo, Hans-Paul Schwefel
Permutations can represent search problems when all points in the search space have unique evaluations. Given a particular set of N evaluations we have N! search algorithms and N! possible functions. A general No Free Lunch result holds for this finite set of N! functions. Furthermore, it is proven that the average description length over the set of N! functions must be O(N lg N). Thus if the size of the search space is exponentially large with respect to a parameter set which specifies a point in the search space, then the description length of the set of N! functions must also be exponential on average. Summary statistics are identical for all instances of the set of N! functions, including mean, variance, skew and other r-moment statistics. These summary statistics can be used to show that any set of N! functions must obey a set of identical constraints which holds over the set of Walsh coefficients. This also imposes mild constraints on schema information for the set of N! functions. When N = 2 L subsets of the N! functions are related via Gray codes which partition N! into equivalence classes of size 2L.