Mutation rate vs. Population Simulation

darwin.js

// Constants

const M_RATES = [
    0,
    0.001,
    0.01,
    0.1,
];
const POP_SIZE = 100;
const GENERATIONS = 50;
const GENOME_LENGTH = 20;
const FITNESS_FACTOR = 0.8; // on a scale of 0 to 1 higher = more difficult
const LIFETIME = 4; // generations
const FERTILITY = .3;

class Individual {

    constructor(m_rate, genome) {
        this.m_rate = m_rate;
        this.age = 0;

        if (genome) {
            this.genome = genome;
        } else {
            this.genome = [];
            for (let i = 0; i < GENOME_LENGTH; i ++) {
                this.genome.push(Math.random());
            }
        }
    }

    is_fit() {
        // To be "fit", 90% of genes have to have value > FITNESS_FACTOR
        let fit_genes_count = 0;
        for (const gene of this.genome) {
            if (gene > FITNESS_FACTOR) fit_genes_count ++;
        }
        return fit_genes_count > (0.2 * this.genome.length);
    }

    do_age() {
        this.age ++;
    }

    clone() {
        const n_ind = new Individual(this.m_rate, this.genome.slice());
        for (let i = 0; i < GENOME_LENGTH; i ++) {
            if (Math.random() < this.m_rate) {
                n_ind.genome[i] = Math.random();
            }
        }
        return n_ind;
    }

}

class Population {

    constructor(size, m_rate) {
        this.size = size;
        this.m_rate = m_rate;
        this.population = [];
        this.generation = 0;
        for (let i = 0; i < size; i ++) {
            this.population.push(new Individual(m_rate));
        }
    }

    get_avg_fitness() {
        let sum = 0;
        for (const individual of this.population) {
            if (individual.is_fit()) sum ++;
        }
        return sum / this.population.length;
    }

    /**
     * Pass one generation, killing off unfit organisms
     */
    age_generation() {
        for (const individual of this.population) {
            individual.do_age();

            if (Math.random() < FERTILITY) {
                this.population.push(individual.clone());
            }

            if (individual.age >= LIFETIME) {
                this._remove_individual(individual);
            }
        }
        this.generation ++;
    }

    _remove_individual(individual) {
        this.population.splice(this.population.indexOf(individual), 1);
    }

}

function main() {
    // create populations
    const populations = [];
    for (const rate of M_RATES) {
        populations.push(new Population(POP_SIZE, rate));
    }

    for (let i = 0; i < GENERATIONS; i ++) {
        // loops
        for (const pop of populations) {
            pop.age_generation();
        }

        console.log(
            populations.map(p => p.population.length).join('\t')
            + '\t'
            + populations.map(p => p.get_avg_fitness()).join('\t')
        );
    }
}

main();