evolving neural network agents in the nero video game
DESCRIPTION
Evolving Neural Network Agents in the NERO Video Game. Author : Kenneth O. Stanley, Bobby D. Bryant, and Risto Miikkulainen Presented by Yi Cheng Lin. Outline. Introduction The behavior of agents Challenges to traditional Reinforcement learning (RL) techniques - PowerPoint PPT PresentationTRANSCRIPT
Evolving Neural Network Agents in the NERO Video Game
Author: Kenneth O. Stanley, Bobby D. Bryant, and Risto Miikkulainen
Presented by Yi Cheng Lin
Outline
Introduction The behavior of agents Challenges to traditional Reinforcement learn
ing (RL) techniques Real-time NeuroEvolution of augmenting Top
ologies (rtNEAT) NeuroEvolving Robotic Operatives (NERO) Playing NERO Conclusion
Introduction
The world video game market in 2002 was between $15 billion and $20 billion
This paper introduces the real-time NeuroEvolution of Augmenting Topologies (rt-NEAT)
It’s purpose is let Non-player-character (NPC) interact with palyers in game playing
The behavior of agents
The behavior of agents in current games is often repetitive and predictable
Machine learning could potentially keep video games interesting by allowing agents to change and adapt
a major problem with learning in video games is that if behavior is allowed to change, the game content becomes unpredictable
Challenges to traditional Reinfor -cement learning (RL) techniques
Large state/action space Diverse behaviors Consistent individual behaviors Fast adaptation Memory of past states
Real-time NeuroEvolution of augmenting Topologies (rtNEAT)
The rtNEAT method is based on NEAT, a technique for evolving neural networks for complex reinforcement learning task using a genetic algorithm
NEAT is based on three key idea
NEAT
First, tracking genes with historical markings to allow easy crossover between different topologies
each unique gene in the population is assigned a unique innovation number, and the number are inherited during crossover
protecting innovation via speciation
NEAT
Second, the reproduction mechanism for NEAT is explicit fitness sharing, where organisms in the same species must share the fitness of their niche, preventing any one species from taking over the population
Third, NAET begins with a uniform population of simple networks with no hidden nodes
Running NEAT in Real Time
rtNEAT
After every n ticks of the game clock, rtNEAT performs the following operation:
Step 1: Remove the agent with the worst adjusted fitness from the population assuming one has been alive sufficiently long so that it has been properly evaluated
It is also important not to remove agents that are too young
rtNEAT
Step 2: Re-estimate F for all species (F : average fitness)
Step 3:Choose a parent species to create the new offspring ,where is the average fitness of species k, is the sum of all the average species fitness
rtNEAT
Step 4: Adjust compatibility threshold Ct dynamically and reassign all agents to species– the advantage of this kind of dynamic compatibilit
y thresholding is that it keeps the number of species relatively stable
Step 5: Replacing the old agent with the new one
Determining Ticks Between Replacements
The appropriate frequency can be determined through a principled approach
Parameter:– n : the ticks between replacements– I : the fraction of the population that is too young
and therefore cannot be replaced– m : is the minimum time alive– |P| is the population size
Determining Ticks Between Replacements
It is best to let the user choose I because in general it is most critical to performance
rtNEAT can determine the correct number of ticks between replacements n to maintain a desired eligibility level.
In NERO, 50% of the population remains eligible using this technique
NeuroEvolving Robotic Operatives (NERO)
Training Mode– The player sets up training exercises by placing o
bjects on the field and specifying goals through several sliders
Battle Mode
Avoiding turret fire
Navigating a maze
Conclusion
A real-time version of NEAT (rtNEAT) was developed to allow users to interact with evolving agents
Using this method, it was possible to build an entirely new kind of video game, NERO, where the characters adapt in real time in response to the player’s actions