NEAT-Python

NEAT (NeuroEvolution of Augmenting Topologies) is an algorithm developed by Ken Stanley that applies genetic algorithms to machine learning.

1. Generates a population of genomes (neural networks)
2. Clusters genomes into species based on their genomic distances
3. Evaluates the fitness score of each genome
4. Breeds and mutates the best genomes over the course of generations

This implementation is a modified version of the algorithm written in Python.

Here is the original paper. Below is an animation of the flappy_ai.py demo script.

Dependencies

None. Just the standard Python libraries.

Installation

To install via pip, simply enter pip install git+https://github.com/SirBob01/NEAT-Python.git on the console.

Basic Usage

Import the NEAT module.

from neat import neat

Set the hyperparameters of the model. See the source code for the complete list of tweakable values.

hp = neat.Hyperparameters()
hp.max_generations = 100
hp.distance_weights["bias"] = 0.4
hp.mutation_probabilities["weight_perturb"] = 0.3

Generate the genomic population of a new brain, denoting the number of inputs and outputs respectively, as well as its population count, for its base parameters.

# Takes 3 inputs, produces 2 outputs
brain = neat.Brain(3, 2, population=100, hyperparams=hp)
brain.generate()

Training genomes can be done in two ways. The first way is via manual iteration:

while brain.should_evolve():
    genome = brain.get_current()
    output = genome.forward([0.3, 0.1, 0.25])

    genome.set_fitness(score(output)) # score() returns a numerical fitness value
    
    brain.next_iteration() # Next genome to be evaluated

The second way is to use NEAT-Python's multiprocessing functionality.

def score(genome, some_arg, some_kwarg=None):
    """Calculate the fitness of this genome."""
    output = genome.forward([0.3, 0.1, 0.25])
    example_fitness = sum(output)
    
    print(some_arg, some_kwarg)
    return example_fitness
    
while brain.should_evolve():
    brain.evaluate_parallel(score, 3, some_kwarg="Hello!") # 3, Hello!

For both methods, the brain's .should_evolve() function determines whether or not to continue evaluating genomes based on the maximum number of generations or fitness score to be achieved.

A genome's .forward() function takes a list of input values and produces a list of output values. These outputs may be evaluated by a fitness function and the fitness score of this current genome may be updated via the genome's .set_fitness() method.

Note that the fitness function must be a maximization function, and all values must strictly be non-negative.

To grab a clone of the best performing genome in the population, use the brain's .get_fittest() function.

Finally, a brain and all its neural networks can be saved to disk and loaded. Files are automatically read and saved as .neat files.

brain.save('filename')
loaded_brain = neat.Brain.load('filename') # Static method

Read NEAT's doc-strings for more information on the module's classes and methods.

TODO

• Implement interspecies sexual crossover
• Fix bugs in repopulation algorithm
• Allow mutable activation functions for each node (heterogeneous activations)

License

Code and documentation Copyright (c) 2018-2020 Keith Leonardo

Code released under the BSD 3 License.