Population

The Population class is responsible for managing a collection of genomes and evolving them through generations using the NEAT algorithm. It handles speciation, fitness evaluation, selection, and reproduction to improve solutions over time.

Properties

Property	Type	Description
genomes	Array	Collection of all genomes in the current generation
species	Array	Collection of species containing genomes grouped by similarity
populationId	String/Number	Unique identifier for the population
generation	Number	Current generation number
config	Object	Configuration parameters for the population

Constructor

javascript

new Population(config)

Creates a new population with genomes initialized according to the provided configuration.

Parameter	Type	Description
config	Object	Configuration object containing parameters for the population and NEAT algorithm

Methods

evolve

javascript

population.evolve() → void

Advances the population to the next generation by performing the complete evolutionary process. This includes speciation, stagnation handling, selection, reproduction, and elite preservation.

The evolve method performs the following steps:

Assigns genomes to species based on genetic similarity
Tracks innovation numbers for new genes
Preserves elite genomes from each species
Handles stagnation by removing underperforming species
Removes worst-performing genomes from each species
Calculates how many offspring each species should produce
Generates offspring through crossover and mutation
Adds elite genomes back into the new generation
Replaces the current generation with the new one
Increments the generation counter

javascript

// Create and evolve a population for 100 generations
const population = new Population(config);

for (let i = 0; i < 100; i++) {
  // Evaluate all genomes in the population
  population.evaluatePopulation();

  // Display information about the current generation
  const bestGenome = population.getBestGenome();
  console.log(`Generation ${i}: Best fitness = ${bestGenome.fitness}`);

  // Evolve to the next generation
  population.evolve();
}

Note

The evolve() method does not evaluate the fitness of genomes. You must call evaluatePopulation() or set the fitness manually before evolve() to ensure fitness values are calculated for the current generation.

evaluatePopulation

javascript

population.evaluatePopulation() → void

Evaluates the fitness of all genomes in the population using the fitness function provided in the configuration. This method must be called before evolve() to ensure proper selection and reproduction based on fitness values.

The fitness function should be defined in the configuration object and will be applied to each genome in the population. If a fitness function is not provided, you will need to manually assign fitness values to each genome.

speciate

javascript

population.speciate() → void

Divides the population into species based on the genetic similarity between genomes. Genomes are grouped into species when their compatibility distance is below the compatibility threshold defined in the configuration.

getBestGenome

javascript

population.getBestGenome() → Genome

Returns the genome with the highest fitness value in the current population.

Returns	Type	Description
bestGenome	Genome	The genome with the highest fitness in the population

javascript

// Get the best genome from the population
const bestGenome = population.getBestGenome();
console.log(`Best fitness: ${bestGenome.fitness}`);

// Propagate the genome
const output = bestGenome.propagate([1, 0]);