population.js

class Population {
	constructor(size) {
      	this.size = size;
    	this.players = [];
      
      	// probability that a child is created by crossing over
      	this.crossoverRate = 0.75;
      	// probability that mutation occurs 
      	this.mutationRate = 0.05;
      
      	this.initPlayers();
    }
  
  	initPlayers() {
    	for (let i = 0; i < this.size; i++) {
        	this.players[i] = new Player();
        }
    }
  
  	update() {
    	for (let i = 0; i < this.players.length; i++) {
        	this.players[i].update();
        }
      
      	if (this.allDead()) {
        	this.evolve();
        }
    }
  
  	show() {
    	for (let i = 0; i < this.players.length; i++) {
        	this.players[i].show();
        }
    }
  
  	allDead() {
    	for (let i = 0; i < this.players.length; i++) {
        	if (!this.players[i].isDead) {
            	return false;
            }
        }
      	return true;
    }
  
  	evolve() {
      	let newPlayers = [];
      
    	this.calculateFitnesses();
      
      	for (let i = 0; i < this.players.length - 1; i++) {
        	let parent1 = this.selectParent();
          	let parent2 = this.selectParent();
          
          	let childDNA = this.crossover(parent1.neuralNet.toDNA(), parent2.neuralNet.toDNA());
          	this.mutate(childDNA);
          
          	let child = new Player();
          	child.neuralNet = child.neuralNet.fromDNA(childDNA).value;
          
          	newPlayers.push(child);
        }

      	let fittestPlayer = this.players[0];
      	let fitnessRecord = 0;
      
      	for (let i = 0; i < this.players.length; i++) {
        	if (this.players[i].fitness > fitnessRecord) {
            	fittestPlayer = this.players[i];
            }
        }
      
      	newPlayers.push(fittestPlayer);
      
      	this.players = newPlayers;
      
      	gTerrain = new Terrain(900, 350);
    }
  
  	calculateFitnesses() {
    	for (let i = 0; i < this.players.length; i++) {
        	this.players[i].calculateFitness();
        }
    }
  
  	selectParent() {
    	let fitnessSum = 0;
      	
      	for (let i = 0; i < this.players.length; i++) {
        	fitnessSum += this.players[i].fitness;
        }
      
      	let randomNumber = random(fitnessSum);
      	let runningSum = 0;
      
      	for (let i = 0; i < this.players.length; i++) {
        	runningSum += this.players[i].fitness;
          
          	if (runningSum > randomNumber) {
            	return this.players[i];
            }
        }
    }
  
  	crossover(parentDNA1, parentDNA2) {
      	let childDNA = [];
      
    	if (random(1) > this.crossoverRate) {
        	childDNA = parentDNA1.slice(0);
        }
      	else {
        	let splitPoint = int(random(parentDNA1.length));

          	childDNA = parentDNA1.slice(0, splitPoint);
          	childDNA.push(...parentDNA2.slice(splitPoint));
        }
      
      	return childDNA;
    }
  
  	mutate(dna) {
    	for (let i = 0; i < dna.length; i++) {
        	if (random(1) < this.mutationRate) {
            	dna[i] = biolib.Utils.normalizedRandom();
            }
        }
    }
}