Coye Cheshire & Andrew Fiore June 19, 2015 // Computer-Mediated Communication Iterated Prisoner’s Dilemma

6/19/2015Computer-Mediated Communication — Cheshire & Fiore1 Strategizing in repeated PD games  Consider two individuals who interact repeatedly over time 1)No mechanisms for enforceable commitments. 2)No way to be sure what the other will do on each ‘turn’. 3)No way to eliminate the other player or leave the interaction. 4)No way to change the other player’s payoffs. What strategy might you use if you had to play this game over and over again with others? Always Cooperate? Always Defect? Something more complicated, perhaps using past behavior?

6/19/2015Computer-Mediated Communication — Cheshire & Fiore2 CoopDefect Coop3,33,30,50,5 Defect5,05,01,11,1 C C C C C C C C C … versus D D D D D D D D D …

6/19/2015Computer-Mediated Communication — Cheshire & Fiore3 PD tournament  Round-robin format  Each strategy competes one-on-one with every other strategy and itself  Strategy with the most total points wins  Number of turns per game unknown  Other strategies unknown  No persistent memory across games

6/19/2015Computer-Mediated Communication — Cheshire & Fiore4 Writing your strategy  Work in groups of 2–5 people  Need at least one person who knows Java  Need a laptop with a working JDK installation  IPDLX open-source package  Moves represented as doubles  COOPERATE = 1.0, DEFECT = 0.0  Can return fractional values; system will round them  History of your moves, opponent’s moves available — see handout

6/19/2015Computer-Mediated Communication — Cheshire & Fiore5 Time for strategizing…

6/19/2015Computer-Mediated Communication — Cheshire & Fiore6 Tournament time!