methods/selection

Defines various selection methods used in genetic algorithms to choose individuals for reproduction based on their fitness scores.

Selection is a crucial step that determines which genetic traits are passed on to the next generation. Different methods offer varying balances between exploration (maintaining diversity) and exploitation (favoring high-fitness individuals). The choice of selection method significantly impacts the algorithm's convergence speed and the diversity of the population. High selection pressure (strongly favoring the fittest) can lead to faster convergence but may result in premature stagnation at suboptimal solutions. Conversely, lower pressure maintains diversity but can slow down the search process.

Read this file as a compact pressure ladder:

FITNESS_PROPORTIONATE says selection chance should scale with score,
POWER says front-runners should be favored more aggressively than raw proportional scores would imply,
TOURNAMENT says selection pressure should come from repeated local competitions instead of one global roulette view.

Those strategies are not only different implementations. They encode different ideas about what "deserves another child" means in an evolutionary run.

A practical chooser for first experiments:

start with FITNESS_PROPORTIONATE when you want the simplest global interpretation of score share,
move to POWER when the best genomes are emerging but plain roulette pressure is still too gentle,
prefer TOURNAMENT when score scale is noisy, unstable, or hard to compare across the whole population.

Minimal workflow:

const conservativeSelection = selection.FITNESS_PROPORTIONATE;

const aggressiveSelection = {
  ...selection.POWER,
  power: 6,
};

const bracketSelection = {
  ...selection.TOURNAMENT,
  size: 7,
  probability: 0.75,
};

flowchart LR
  Population[Scored population] --> Proportionate[FITNESS_PROPORTIONATE<br/>probability tracks score share]
  Population --> Power[POWER<br/>front of ranking gets extra pressure]
  Population --> Tournament[TOURNAMENT<br/>small local bracket decides]