void Generation::produce_offspring(genetic_parameters const& genetic_param, std::vector<bound> const& param_bounds)
{
// Initialize random generator
std::random_device rd;
std::array<unsigned int, std::mt19937::state_size> seed_data;
std::generate_n(seed_data.begin(), seed_data.size(), std::ref(rd));
std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
std::mt19937 engine(seq);
// Check if the number of chromosomes is even
size_t pairs(0);
if (size % 2 == 0) {
pairs = size / 2;
}
else {
pairs = (size + 1) / 2;
}
// Select the pairs of parents and produce an offspring
for (size_t i = 0; i < pairs; ++i) {
// Select parents via tournament selection
Chromosome parent1 = chromosomes[tournament_selection(engine)];
Chromosome parent2 = chromosomes[tournament_selection(engine)];
// Crossover parents
crossover_chromosomes(parent1, parent2, genetic_param.prob_crossover, engine);
// Mutate parents
mutate_chromosome(parent1, genetic_param.prob_mutation, param_bounds, engine);
mutate_chromosome(parent2, genetic_param.prob_mutation, param_bounds, engine);
// Save new chromosomes
offspring.push_back(parent1);
if (2 * (i + 1) <= size) {
offspring.push_back(parent2);
}
}
// Save new generation
chromosomes = offspring;
offspring.clear();
}
void perform_crossover_and_mutation(int parent1_index, int parent2_index,
int nextpopindex)
/* Performs crossover between the given parents, and mutates the offspring */
{
int i,j, toggle, max_parent, site;
int *crossover_template, *child_1, *child_2;
struct element *new_top;
#if GA_DEBUG
printf("In` perform_crossover_and_mutation with parent index: %d, %d\n",
parent1_index, parent2_index);
print_a_chromosome(current_pop[parent1_index].chrom);
printf("\n");
print_a_chromosome(current_pop[parent2_index].chrom);
#endif
child_1 = (void *)my_malloc(CHROM_LENGTH * sizeof(int));
child_2 = (void *)my_malloc(CHROM_LENGTH * sizeof(int));
crossover_template = (void *)my_malloc(CHROM_LENGTH * sizeof(int));
/* initialize crossover_template */
for (j = 0; j < CHROM_LENGTH; j++)
crossover_template[j] = ZERO;
/* First decide whether or not to cross over */
if (knuth_random() < CROSSOVER_RATE) {
#if GA_DEBUG
printf("Decided to cross over\n");
#endif
/* Put ones in the template array where there are crossover sites */
for (j = 0; j < CROSSOVER_SITES; j++) {
/* Definitely choose a site at which to cross over */
site = (knuth_random() * (CHROM_LENGTH -1)) + 1;
if (crossover_template[site]==ONE)
j--;
else
crossover_template[site] = ONE;
}
}
else {
#if GA_DEBUG
printf("Decided not to perform crossover\n");
#endif
/* Make sure crossover template is all ZEROS */
for (j=0; j < CHROM_LENGTH; j++)
if (crossover_template[j] != ZERO) {
fprintf(stderr, "Error: Decided not to perform crossover, but crossover template has non-zero\n");
exit(1);
}
}
#if GA_DEBUG
printf("Here is the crossover template\n");
for (i=0; i < CHROM_LENGTH; i++)
printf("%d", crossover_template[i]);
printf("\n");
#endif
/* Begin crossing-over. If it was decided not to cross over, then
* crossover_template is all zeros.
*/
toggle = 0; /* this gets switched when we hit a crossover site */
for (j = 0; j < CHROM_LENGTH; j++) {
if (crossover_template[j]==ONE)
toggle = toggle ? 0 : 1;
if (toggle)
{
child_2[j] = current_pop[parent1_index].chrom[j];
child_1[j] = current_pop[parent2_index].chrom[j];
}
else
{
child_1[j] = current_pop[parent1_index].chrom[j];
child_2[j] = current_pop[parent2_index].chrom[j];
}
}
#if GA_DEBUG
printf("After crossover (or not), here are the two children:\n");
print_a_chromosome(child_1);
printf("\n");
print_a_chromosome(child_2);
#endif
/* Perform mutation operator on the two */
mutate_chromosome(child_1);
mutate_chromosome(child_2);
#if GA_DEBUG
printf("After mutation, here are the two children:\n");
print_a_chromosome(child_1);
printf("\n");
print_a_chromosome(child_2);
printf("\n We will put them at indices %d and %d\n",
nextpopindex, nextpopindex+1);
#endif
/* We now have two fine children */
/* Put child_1 in next_pop */
for (j = 0; j < CHROM_LENGTH; j++)
next_pop[nextpopindex].chrom[j] = child_1[j];
next_pop[nextpopindex].generation = current_generation+1;
next_pop[nextpopindex].id = nextpopindex;
nextpopindex++;
/* Put child_2 in next_pop */
for (j = 0; j < CHROM_LENGTH; j++)
next_pop[nextpopindex].chrom[j] = child_2[j];
next_pop[nextpopindex].generation = current_generation+1;
next_pop[nextpopindex].id = nextpopindex;
#if GA_DEBUG
printf("Children have been put in next pop\n");
#endif
#if GA_DEBUG
printf("About to free pointers\n");
#endif
/* Free pointers */
free(child_1);
free(child_2);
free(crossover_template);
}
