selection.md

Selection Operators Reference

Selection operators choose parents for reproduction.

Module

use fugue_evo::operators::selection::{
    TournamentSelection, RouletteWheelSelection, RankSelection
};

Tournament Selection

Select best from k random individuals.

let selection = TournamentSelection::new(k);

Parameter	Type	Description
k	usize	Tournament size

Characteristics:

• Higher k = more selection pressure
• k=2 is minimal pressure
• k=5-7 for high pressure
• Efficient: O(k) per selection

Example:

let selection = TournamentSelection::new(3);
// Selects best of 3 random individuals

Roulette Wheel Selection

Probability proportional to fitness.

let selection = RouletteWheelSelection::new();

Characteristics:

• Fitness proportionate
• Can lose selection pressure with similar fitnesses
• Sensitive to fitness scaling
• O(n) setup, O(log n) per selection

Requirements:

• Fitness must be positive
• Works best with transformed fitness

Rank Selection

Probability based on fitness rank.

let selection = RankSelection::new();
// or with pressure parameter
let selection = RankSelection::with_pressure(2.0);

Parameter	Type	Default	Description
pressure	f64	2.0	Selection pressure (1.0-2.0)

Characteristics:

• Robust to fitness scaling
• Maintains selection pressure
• O(n log n) for ranking
• Good for multimodal problems

Comparison

Operator	Pressure Control	Scaling Sensitive	Efficiency
Tournament	Tournament size	No	O(k)
Roulette	Fitness transformation	Yes	O(log n)
Rank	Pressure parameter	No	O(n log n)

Usage

SimpleGABuilder::<RealVector, f64, _, _, _, _, _>::new()
    .selection(TournamentSelection::new(3))
    // ...

See Also

• Custom Operators - Create custom selection