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Hi all > The gpsemantics readme file seems to be errant. apologies -- not sure how I failed to include the README file. I'll paste it below (not attach, in case the list doesn't like attachments). James -- Dr. James McDermott, Q237, Lochlann Quinn School of Business, University College Dublin, Ireland. Phone +353 1 716 4731 http://jmmcd.net http://www.ucd.ie/cba/members/jamesmcdermott/ # Copyright 2012 by James McDermott # Licensed under the Academic Free License version 3.0 # See the file "LICENSE" for more information The Order and Majority problems are taken from "Where does the good stuff go, and why? How contextual semantics influences program structure in simple genetic programming" Goldberg, D. and O'Reilly, U.M., in EuroGP 1998. The Order and Majority problems each use the same tree-based representation. There is a single binary non-terminal, "J", or "Join". For a problem of size n (which is tunable), there are 2(n+1) terminals, X0, X1, .. Xn and N0, N1, .. Nn. Ni has the sense of ~Xi. The two problems define two different mappings from a tree genotype to a linear phenotype. In both cases, we begin with an empty-list phenotype and traverse the tree in a depth-first left-to-right manner. It doesn't matter whether it's preorder, inorder, or postorder because we ignore the non-terminals. We "express" the terminals by appending them to the phenotype as follows. For Order, for each index i, the first terminal of that index encountered during traversal is expressed (whether it is Xi or Ni). Later terminals of the same index are ignored. For Majority, for each index i, Xi is expressed if there is at least one Xi in the traversal, and there are at least as many Xi as there are Ni. For both problems, the phenotype to fitness mapping is the same: just count the number of occurences of Xi terminals.