Genetic Programming: Hypothesis Evolution By Nam Nguyen Greg Nelson

Introduction To Evol An attempt to more directly simulate the process of natural selection. The system is set up as a large board with agents and examples. Each agent executes on its own thread. Agents live on the board and wander around processing examples and interacting with other agents. Two kinds of agents: helpers and fighters. Examples act as food for the agents.

Goal Implement a new genetic algorithm that, rather than being based on probabilities, actually models the process of natural selection. Build a dynamic, intuitive learning system that very closely emulates natural selection. Find a balance in parameter settings (how much "life" an agent starts with, what the "age" threshold is in order to breed, how much an agent's "life" is boosted by eating an example, etc...); some settings cause agents to breed like rabbits and grow to doomsday, others lead to almost immediate extinction.

Problem Representation Environment is represented by a board. All entities live on this board. Agents walk around, eat examples, breed, share information, and fight with other agents. E E

Hierarchy Tree Entity Example Agent Helper Fighter

Play Tennis Example Example 1 (Outlook = Sunny) && (Temp = Hot) && (Humidity = High) && (Wind = Weak) Then (PlayTennis = Yes) Bit string (First three bits for Outlook, etc…) All hypotheses and examples are represented with this notation.

Agents The agents contain a genotype and phenotype. Both represent hypotheses. The phenotype is used (and changed); the genotype is inherited from birth, never changed, and passed on to future generations. Agents also interact by breeding, helping each other, or fighting.

Examples Continued Examples are created from the training data set and act as food for the agents. When an agent comes upon an example it does one of two things: 1. If it classifies it correctly, it "eats" it, which increases its strength and likelihood for survival. 2. If not, it tries to learn something from it (change some of the phenotype bits to match the example’s).

When Helpers Meet Other Helpers Helper Helper

You are too young. We should help each other. Okay, let’s be friends! Helper Helper

This is what I learned Here’s my knowledge Helper Helper Bit 5 is true Bit 6 is true

When Helpers Meet Other Helpers: part 2 Helper 1 Life 500 Helper 2 Life 800

How old are you?

I am above threshold

Censored

Helper 1 Life 250 Helper 2 Life 550 Helper 3 (Baby) Life 500 Several Cycles Later…

When Fighters Meet Other Agents Fighter 1

Quit stealing my mates and examples

No, you stop!

Lightning Bolt

POW! AH HA HA HA!

When Fighters Meet Wise Helpers Helper 1 Life 900 Fighter 1 Life 800

Must… fight!

That agent is too cute to bully… Hello! How are you?

Get over here!

Zip! AHHHHH!

Whoos h

Smooch!

Helper 1 Life 650 Fighter 1 Life 550 Fighter 2 Baby Life 500 Several Cycles Later…..

Learning Algorithm Agents move around the board learning from examples and each other. The more successful agents will breed more readily, while the less successful agents will be killed by starvation and combat.

Performance Seemed to learn simple tasks such as playTennis and mushroom. - classified 80% of the playTennis set correctly - classified 92% of mushroom test set correctly. This is because it “learned” to classify everything as edible. Performed dismally on other tasks such as voting. Varying parameters might improve stability and speedup convergence.

Problems Population control (doomsday and extinction, memory issues). Too much interaction between agents, not enough eating! Disturbing bug (fixed): agents would have a child and then immediately mate with it!

Conclusions Hard to control/predict a dynamic population of agents acting independently. Nondeterministic: different results every time, although similar trends (above). With lots of work, we think this could work very well.

Sample log file. (Fighter3, ) at [12,3] ate (person161,99) at [12,3] (Fighter3, ) at [12,3] ate (person161,98) at [12,3] (Fighter0, ) at [20,1] is breeding with (Helper0, ) at [20,1]! (Fighter0, ) at [20,1] begat (Fighter20,500000) at [20,1]! (Fighter20,499999) at [19,1] beat up (Fighter19,499987) at [19,1]! (Fighter19,499987) at [19,1] is dying! (Fighter0, ) at [20,2] is breeding with (Helper0, ) at [20,2]! (Fighter0, ) at [20,2] begat (Fighter21,500000) at [20,2]! (Fighter21,500000) at [20,2] got beat up by (Fighter0, ) at [20,2] (Fighter21,500000) at [20,2] is dying! (Helper1, ) at [18,0] ate (person77,98) at [18,0] (Fighter0, ) at [21,4] is breeding with (Helper0, ) at [21,4]! (Fighter0, ) at [21,4] begat (Fighter22,500000) at [21,4]! (Fighter3, ) at [18,0] ate (person77,97) at [18,0] (Helper2, ) at [5,16] ate (person112,99) at [5,16] (Fighter3, ) at [18,24] ate (person52,95) at [18,24] (Helper2, ) at [6,17] ate (person130,100) at [6,17].

Sample output Time limit reached: terminating. The following 42 rules were learned from the training set: Helper1, RANK 2670: IF ((handicappedkids=y) OR (handicappedkids=n)) AND... AND ((export_act_safrica=y)) THEN Democrat.

Questions… ???