From 81dd1ec095657d49a49ca63c431af23f497b0b36 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@ditigal.xyz>
Date: Sun, 16 Nov 2025 19:54:48 +0100
Subject: [PATCH] feat: add stochastic ranking

---
 codes/eoa_lib/src/constraints.rs | 139 ++++++++++++++++++++++++++++++-
 1 file changed, 137 insertions(+), 2 deletions(-)

diff --git a/codes/eoa_lib/src/constraints.rs b/codes/eoa_lib/src/constraints.rs
index 18706f5d31ae9d198513280d3c58819ba7fe2e7a..454bc9d7608124e32555eb76689601ea2dc5a11f 100644
--- a/codes/eoa_lib/src/constraints.rs
+++ b/codes/eoa_lib/src/constraints.rs
@@ -1,8 +1,9 @@
 use std::{collections::VecDeque, convert::Infallible, error::Error};
 
+use rand::{Rng, RngCore};
 use thiserror::Error;
 
-use crate::{comparison::BetterThanOperator, crossover::Crossover, evolution::EvolutionStats, fitness::FitnessFunction, pairing::Pairing, perturbation::PerturbationOperator, population::EvaluatedPopulation, replacement::Replacement, selection::Selection};
+use crate::{comparison::{BetterThanOperator, MinimizingOperator}, crossover::Crossover, evolution::EvolutionStats, fitness::FitnessFunction, pairing::Pairing, perturbation::PerturbationOperator, population::{EvaluatedChromosome, EvaluatedPopulation, Population}, replacement::Replacement, selection::Selection};
 
 pub trait ConstraintFunction {
     type Chromosome;
@@ -223,8 +224,142 @@ pub fn evolve_constraint_penalty_weight_tau_target
         }
 }
 
+#[derive(PartialEq, Debug)]
+pub struct ConstrainedEvaluation<const CONSTRAINTS: usize, TOut> {
+    fitness: TOut,
+    constraints: [TOut; CONSTRAINTS],
+    weighted_sum: TOut
+}
+
+impl<const CONSTRAINTS: usize, TOut: PartialOrd> PartialOrd for ConstrainedEvaluation<CONSTRAINTS, TOut> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        self.weighted_sum.partial_cmp(&other.weighted_sum)
+    }
+}
+
+pub struct ConstrainedEvalFitness<'a,
+    const CONSTRAINTS: usize,
+    TIn,
+    TOut,
+    TFitness: FitnessFunction<In = TIn, Out = TOut>,
+    TConstraint: ConstraintFunction<Chromosome = TIn, Out = TOut>> {
+    fitness: &'a TFitness,
+    constraints: [&'a TConstraint; CONSTRAINTS],
+    constraint_weights: Vec<TOut>
+}
+
+impl <'a,
+      const CONSTRAINTS: usize,
+      TOut: std::ops::Mul<Output = TOut> + std::ops::AddAssign + Copy,
+      TIn,
+      TFitness: FitnessFunction<In = TIn, Out = TOut>,
+      TConstraint: ConstraintFunction<Chromosome = TIn, Out = TOut>>
+    FitnessFunction for ConstrainedEvalFitness<'a, CONSTRAINTS, TIn, TOut, TFitness, TConstraint> {
+    type In = TFitness::In;
+    type Out = ConstrainedEvaluation<CONSTRAINTS, TOut>;
+    type Err = ConstrainedFitnessErr<TFitness::Err, TConstraint::Err>;
+
+    fn fit(self: &Self, inp: &Self::In) -> Result<Self::Out, Self::Err> {
+        let fit = match self.fitness.fit(inp) {
+            Ok(fit) => fit,
+            Err(err) =>
+                return Err(ConstrainedFitnessErr::FitnessErr(err))
+        };
+        let mut weighted_sum = fit;
+        let mut constraints = [fit; CONSTRAINTS];
+
+        for (i, (constraint, weight)) in self.constraints.iter().zip(self.constraint_weights.iter()).enumerate() {
+            let constraint = match constraint.evaluate(inp) {
+                Ok(constraint) => constraint,
+                Err(err) =>
+                    return Err(ConstrainedFitnessErr::ConstraintErr(err))
+            };
+            constraints[i] = constraint;
+            weighted_sum += weight.clone() * constraint;
+        }
+
+        Ok(ConstrainedEvaluation {
+            fitness: fit,
+            constraints,
+            weighted_sum
+        })
+    }
+}
+
+fn stochastic_ranking_sort<const CONSTRAINTS: usize, TIn, TOut: PartialOrd + Default>(
+    evaluations: &[EvaluatedChromosome<TIn, ConstrainedEvaluation<CONSTRAINTS, TOut>>],
+    N: usize,
+    p: f64,
+    better_than: &(impl BetterThanOperator<TOut> + ?Sized),
+    rng: &mut dyn RngCore
+) -> Vec<usize> {
+    let mut indices = (0..evaluations.len()).collect::<Vec<_>>();
+    for _ in 0..N {
+        for j in 0..evaluations.len()-1 {
+            let u = rng.random_range(0.0..=1.0);
+
+            let current_evaluation = &evaluations[indices[j]].evaluation;
+            let next_evaluation = &evaluations[indices[j + 1]].evaluation;
+
+            if (current_evaluation.weighted_sum == Default::default() && next_evaluation.weighted_sum == Default::default()) || u < p {
+                if better_than.better_than(&next_evaluation.fitness, &current_evaluation.fitness) {
+                    indices.swap(j, j + 1);
+                }
             } else {
-                fitness.constraints_weight *= c;
+                if current_evaluation.weighted_sum > next_evaluation.weighted_sum {
+                    indices.swap(j, j + 1);
+                }
             }
         }
+    }
+
+    indices
+}
+
+pub struct StochasticRankingSelection<TSelection, TBetterThan> {
+    N: usize,
+    p: f64,
+    selection: TSelection,
+    better_than: TBetterThan
+}
+
+const MINIMIZING_OPERATOR: MinimizingOperator = MinimizingOperator;
+
+impl<const CONSTRAINTS: usize,
+     TChromosome,
+     TResult: PartialOrd + Default,
+     TSelection: Selection<(), usize>,
+     TBetterThan: BetterThanOperator<TResult>>
+    Selection<TChromosome, ConstrainedEvaluation<CONSTRAINTS, TResult>> for StochasticRankingSelection<TSelection, TBetterThan> {
+    fn select(&self,
+              count: usize,
+              evaluations: &EvaluatedPopulation<TChromosome, ConstrainedEvaluation<CONSTRAINTS, TResult>>,
+              _: &dyn BetterThanOperator<ConstrainedEvaluation<CONSTRAINTS, TResult>>,
+              rng: &mut dyn RngCore
+    ) -> impl Iterator<Item = usize> {
+        let sorted_indices = stochastic_ranking_sort(
+            evaluations.population.as_slice(),
+            self.N, self.p, &self.better_than, rng
+        );
+        let mut rankings = vec![EvaluatedChromosome {
+            chromosome: (),
+            evaluation: 0
+        }; evaluations.population.len()];
+
+        for (ranking, index) in sorted_indices.into_iter().enumerate() {
+            rankings[index] = EvaluatedChromosome {
+                chromosome: (),
+                evaluation: ranking
+            };
+        }
+
+        // Replace with this better than
+        self.selection.select(
+            count,
+            &EvaluatedPopulation::from_vec(rankings),
+            &MINIMIZING_OPERATOR,
+            rng)
+            .collect::<Vec<_>>()
+            .into_iter()
+    }
 }