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//! This module contains the Selection trait and the provided selection functions.
use rand::distributions::{Standard, Uniform};
use rand::prelude::*;
use rayon::prelude::*;
use std::ops::Range;
use std::sync::mpsc::channel;
use SelectionFunctions::*;
/// This trait defines the select function used to select individuals for crossover.
pub trait Selection: Send + Sync {
/// Returns a vector with the indices of the selected individuals according to
/// the fitness of the population and the selection rate.
fn select(&self, fitnesses: &[f64], selection_rate: usize) -> Vec<usize>;
}
/// Defines the number of tournaments parameter.
pub struct NTournaments(pub usize);
/// Provided selection functions
pub enum SelectionFunctions {
/// Roulette function.
Roulette,
/// Tournaments function.
Tournaments(NTournaments),
/// Cup function, a cup tournament where the `selection_rate` first phases
/// of the tournament are selected (winner, final, semifinal, etc.).
Cup,
}
impl Selection for SelectionFunctions {
fn select(&self, fitnesses: &[f64], selection_rate: usize) -> Vec<usize> {
match self {
Roulette => {
let mut rgen = SmallRng::from_entropy();
let mut winners = Vec::with_capacity(selection_rate);
let mut probs = Vec::with_capacity(fitnesses.len());
let fitness_sum: f64 = fitnesses.iter().sum();
for fit in fitnesses {
probs.push(fit / fitness_sum);
}
for _i in 0..selection_rate {
let random: f64 = rgen.sample(Standard);
let mut accum = 0_f64;
for (ind, p) in probs.iter().enumerate() {
if random <= accum + p {
winners.push(ind);
break;
}
accum += p;
}
}
winners
}
Tournaments(n_tournaments) => {
let (sender, receiver) = channel();
let mut winners = Vec::with_capacity(n_tournaments.0);
Range {
start: 0,
end: n_tournaments.0,
}
.into_par_iter()
.for_each_with(sender, |s, _t| {
let mut rgen = SmallRng::from_entropy();
let mut fighters = Vec::with_capacity(selection_rate);
for _f in 0..selection_rate {
let sel = rgen.sample(Uniform::from(0..fitnesses.len()));
fighters.push((sel, fitnesses[sel]));
}
s.send(
fighters
.par_iter()
.max_by(|x, y| x.1.partial_cmp(&y.1).unwrap())
.unwrap()
.0,
)
.unwrap();
});
for win in receiver {
winners.push(win);
}
winners
}
Cup => {
let mut rgen = SmallRng::from_entropy();
let mut winners = Vec::with_capacity(2_i32.pow(selection_rate as u32) as usize - 1);
let n_phases = (fitnesses.len() as f64).log2() as usize + 1;
let mut phases: Vec<Vec<(usize, f64)>> = Vec::with_capacity(n_phases);
// Initialize the phases members
for i in 0..n_phases {
let size = 2_i32.pow(i as u32) as usize;
phases.push(Vec::with_capacity(size));
for _j in 0..size {
phases[i].push((0, 0_f64));
}
}
// Randomly initialize the last phase
let mut candidates = Vec::with_capacity(fitnesses.len());
for f in fitnesses {
candidates.push(*f);
}
{
let last_phase = &mut phases[n_phases - 1];
let mut i = 0;
while i < last_phase.len() {
let sel = rgen.sample(Uniform::from(0..candidates.len()));
last_phase[i] = (sel, candidates[sel]);
candidates.remove(sel);
i += 1;
}
}
// Do the fights
Self::cup_phase_fight(&mut phases, n_phases - 1);
// Push winners
for phase in phases
.iter()
.enumerate()
.filter(|(i, _p)| *i < selection_rate as usize)
.map(|(_i, p)| p)
{
for winner in phase.iter() {
if winners.is_empty() {
winners.push(winner.0);
} else {
let index = rgen.sample(Uniform::from(0..winners.len()));
winners.insert(index, winner.0);
}
}
}
winners
}
}
}
}
impl SelectionFunctions {
fn cup_phase_fight(phases: &mut Vec<Vec<(usize, f64)>>, phase: usize) {
let (sender, receiver) = channel();
Range {
start: 0,
end: phases[phase].len() / 2,
}
.into_par_iter()
.for_each_with(sender, |s, i| {
let ind1 = i * 2;
let ind2 = ind1 + 1;
if phases[phase][ind1].1 >= phases[phase][ind2].1 {
s.send((i, phases[phase][ind1])).unwrap();
} else {
s.send((i, phases[phase][ind2])).unwrap();
}
});
for (i, child) in receiver {
phases[phase - 1][i] = child;
}
if phase > 1 {
Self::cup_phase_fight(phases, phase - 1);
}
}
}