/* Simple implementation of genetic algorithm. We have a bunch (10) of "living things" that have boolean genes, and we hope to evolve this population so it gets genes that all equal true (total 16). After each generation, the fitness score is outputed and then sorted. Then the top four performers remain and pursue onto next generation, the following six are discarded and replaced by babies of the top four performers. A small probability of mutation is also applied, to encourage evolution after the population all converged to same values. */ import java.lang.Math; import java.util.Comparator; import java.util.Arrays; public class GeneticAlgorithm{ static boolean[] goal={true,true,true,true,true,true,true,true,true,true,true,true,true,true,true,true}; static LivingThing[] population=new LivingThing[10]; public static void main(String[] args) { for(int i=0;i<10;i++){ population[i]=new LivingThing(); } int gen=0; while(population[3].fitness!=16&&gen<30){ System.out.println("\nGeneration "+(gen++)+"\n"); for(int i=0;i<10;i++){ scoreFitness(population[i]); System.out.println(population[i].fitness); } System.out.println("\nsorting\n"); sortFitness(); for(int i=0;i<10;i++){ System.out.println(population[i].fitness); } System.out.println("\nkeep 4 parents and make babies\n"); for(int i=4;i<10;i++){ LivingThing parentA,parentB; if(i%2==0){ parentA=population[0]; parentB=population[1]; }else{ parentA=population[2]; parentB=population[3]; } population[i]=getBaby(parentA,parentB); } } } public static void scoreFitness(LivingThing lt){ lt.fitness=0; for(int i=0;i<16;i++){ if(lt.genes[i]==goal[i]){ lt.fitness++; } } } public static void sortFitness(){ Arrays.sort(population,new SortbyFitness()); } public static LivingThing getBaby(LivingThing a, LivingThing b){ LivingThing[] parents={a,b}; LivingThing baby=new LivingThing(); for(int i=0;i<16;i++){ boolean gene=parents[(int)(Math.random()*2)].genes[i]; if(Math.random()<0.05){ gene=!gene;//mutation from cosmic rays } baby.genes[i]=gene; } return baby; } } class SortbyFitness implements Comparator{ public int compare(LivingThing a, LivingThing b) { return b.fitness - a.fitness; } } public class LivingThing{ public LivingThing(){ for(int i=0;i<16;i++){ int gene=(int)(Math.random()*2); genes[i]=gene==1?true:false; } } boolean[] genes=new boolean[16]; int fitness=0; }

Genetic Algorithm