HIDDEN ORDER Chapter 1: Basic Elements

Complex Adaptive Systems (cas) Aggregates of independent agents Agents behavior governed by a collection of rules Persistence and coherence in the face of change –Dependent on extensive interaction, aggregation of diverse elements, and adaptation and learning i.e. economy, ecosystem, CNS

Objectives Purpose of the book is to formulate a solid theory about complex adaptive systems –Separate fundamental characteristics from idiosyncrasies –Difficult to do because of nonlinearities –Compensate with cross-disciplinary comparisons

Seven Basics Four properties and three mechanisms shared by all cas Not the only shared characteristics. The rest can be built from a combination of these seven

Aggregation (Property) 2 senses 1 st Sense: Constructing Models 2 nd Sense: What cas do –Emergence of complexity from a network of simpler agents. –Aggregates can act as agents in higher-level structures (meta-agents) –i.e. Cells  Tissues  Organs  Organ Systems  Organism

Tagging (Mechanism) A mechanism that facilitates aggregation by bringing like things together –i.e. a flag used to rally a group of people, pheromones and visual patterns that lead to selective mating Allow observation of properties hidden by symmetry. –i.e. painting a stripe on a cue ball to see changes in the axis of rotation

Nonlinearity (Property) A function is linear its value can be calculated by adding the values of its parts. –i.e. A=B+C Nonlinearlity of Pool Ball Example –(B+W)(t+1)=(B+W)+c(B)(W) –(G+W)(t+1)=(G+W)+c’(G)(W) –Can we simplify the model by aggregating B and G into a single category S? (S=B+G) –No. There is no coefficient that works for all combinations of B and G. –If the function was linear, then we could take the average of c and c’

Flow (Property) [node, connector, resource] [phones, phone lines, conversations] Multiplier Effect –Occurs after additional resource is added at a node –Initial effect is multiplied as the resource is passed through the network Recycling Effect –Result of cycles in a network –Recycling with the same input produces a greater output at each node

Diversity (Property) Not random. System will adapt to fill holes. –New agent typically occupies same niche as previous agent and provides most of the missing connections –Leads to convergence in biology i.e. squid vs. mammalian eye –Founder Effect

Diversity (Property) Pattern of diversity in cas is dynamic. Diversity is a product of adaptation. Each new adaptation creates possibilities of new interactions and new niches

Internal Models (mechanism) Allows for anticipation Two types –Tactit: prescribes an action under an implicit prediction of a desired future state i.e. a bacteria swimming up a nutrient gradient –Overt: used as a basis for explicit explorations of alternatives (lookahead) i.e. exploring possible scenarios before moving a chess piece

Building Blocks How are internal models built from constantly changing environments? –Situations are distilled into useful and relevant building blocks –A flat tire while driving a red Saab on the expressway? –Decompose into rules about cars, tires, and expressways

Hidden Order Chapter 2 Adaptive Agents By John Holland

Requirements of Adaptive Agents 1.Performance System - a universal way to represent the capabilities of different agents using messages and conditional rules 2.Rule Discovery - making changes to an agent’s capabilities by means of a credit score

Making Use of Binary A detector receives a message when conditions are met, the result of which triggers an action and completes the rule Messages - strings of 1’s and 0’s of length (L) Conditions - strings 1’s, 0’s and #’s (signifying no specificity), also of length L

Messages from Two Sources 1)Detector Originated - derived from and given meaning by the environment 2)Rule Originated - produced by other rules, given meaning only when they activate effectors

Credit Scores Rules have strength that is like having cash on hand, and can be viewed as being producers, middlemen, or consumers that buy, sell, and trade messages The ultimate consumer is the rule that is active when the agent receives a reward from the environment All rules down the line are credited and automatically strengthened

Building Blocks Rules can be divided into building blocks called schemata. Successful rules have schemata that in general serve as better building blocks than random binary strings Successful schemata are singled out by replacing other parts of the sequence with the * symbol

Crossing Over Binary sequences are crossed over using the genetic algorithm Short schemata are conserved through probability Longer schemata are preserved because they are composed of shorter successful schemata that appear in a large portion of the gene pool

Mutation Successful rules can become fixed in a population before other more successful rules can be discovered Random mutations disrupt fixation during crossing over, restoring adaptation

The Prisoner’s Dilemma A game where two players simultaneously decide to defect (D), or cooperate (C) Tit-for-tat is a favorable strategy that produces a relatively large number of points Agents that begin with schemata for tit-for-tat discover better strategies by deciding on whether an opponent is bluffing or not