Project 1

Requirements

Submit a complete technical report on a project about the Iterated Prisoners’ Dilemma that will be presented during the class.

p1 \ p2	cooperate	defect
cooperate	3, 3	0, 5
defect	5, 0	1, 1

Three strategies analyzed:
- ALL-D: always defect, optimizes individual fitness
- ALL-C: always cooperate, optimizes population fitness
- RAND: randomly chooses between defect and cooperate
Expected scores from this analysis:

playing	ALL-C	RAND	ALL-D	Average
ALL-C	3.0	1.5	0.0	1.5
RAND	4.0	2.25	0.5	2.25
ALL-D	5.0	3.0	1.0	3.0

-	Random//Random	Random//Tit For Tat	Random//Pavlov	Tit For Tat//Tit For Tat	Tit For Tat//Pavlov	Pavlov//Pavlov
winner	Random	Random	Pavlov	TIE	TIE	TIE
avg A score	22.7	23.9	18.7	30.0	30.0	30.0
avg B score	23.7	21.9	26.2	30.0	30.0	30.0
A/B avg	0.957806	1.091324	0.71374	1.0	1.0	1.0
all identical?	False	False	False	True	True	True

Uses a darwinism model
Each entity has a fitness function
Each generation selects the most fit individuals to reproduce
Each reproduction produces a new generation with some mutations, traits of predecessors MUST be passed on
Over time, the population will evolve to be more fit

Population of 100 individuals
Chromosome is a 64-bit string representing the strategy of the individual
A bit is a choice depending on cooperate or defect played for a specific configuration of past moves

How do you encode a strategy with a string?

Suppose memory depth is only 1. Then, there are only four choices, based on previous moves:

Now, using 3 previous moves, suppose the memory is this:

Memory	A	B	Code
Move 1	C	C	R
Move 2	D	C	T
Move 3	C	D	R

(RTR = 010 = 5) (I don't get this part but we can just use opponent moves probably)

** Bit string must be 2 ** MEMLEN + MEMLEN long; last MEMLEN bits are reserved for the first few moves.

Fitness: Each player competes against every other for 64 consecutive rounds, and a cumulative score is maintained
Selection: Roulette Wheel selection
Reproduction: Random point crossover with replacement
Mutation rate 0.001
Generations: 1,000 generations

Tit for tat (TFT)
- First move, cooperate
- Always choose opponent's last move as next move
Tit for Two Tat (TFT2)
- First two moves, cooperate
- If the opponent defects twice in a row, choose defection as the next move
Suspicious Tit for Tat (STFT)
- First move, defect
- Always choose opponent's last move as next move
Free Rider (ALL-D)
- ALWAYS defect
Always Cooperate (ALL-C)
- Must I say any more

You will form groups of 3 or 4.