optima-cityu Diverse Island GA Skill
Reference: LLM4AD_Next specialized island model. Extends IslandGA with specialized island roles (a continuous exploitation↔exploration spectrum), adaptive stagnation-aware migration, and novelty preservation.
1. Method Essence
Diverse IslandGA builds on the classic island model but removes the assumption that all islands are identical. Instead, it assigns each island a continuous strategy position along the exploration↔exploitation spectrum, and coordinates them through adaptive migration that fires only when an island stagnates. This keeps the population diverse and avoids the premature spread of a local optimum.
Core mechanisms:
| Concept | Role |
|---|---|
| Island strategy spectrum | island_strategy_strength controls how much islands differ (experience-reuse → novelty exploration) |
| Adaptive migration | adaptive_migration receives migrants only after an island stagnates |
| Stagnation threshold | migration_stagnation_threshold consecutive non-improving generations before migration is allowed |
| Novelty survivor | novelty_survivor_ratio reserves non-elite survivor slots for code-dissimilar individuals |
| Exploration restart | exploration_restart_ratio share of candidates built from scratch on the most exploratory island |
| Short-run guard | short_task_max_migrations caps migration events on short runs |
2. Recommended Parameters
See params.yaml in this directory for the recommended parameter configuration.
Note: This variant ships with a smaller out-of-box workload (max_generations=10, island_population_size=5) than the plain IslandGA, so it is safe to run without heavy tuning.
What Happens During Evolution
- Initialize
num_islandsislands, each at a distinct point on the strategy spectrum - Each island evolves with its own exploration/exploitation bias and memory policy
- Every generation, elites are reevaluated at higher fidelity (
elite_reevaluation_count) - Migration is adaptive: an island may receive migrants only after
migration_stagnation_thresholdnon-improving generations - Novel survivors (low code similarity) are retained to preserve diversity
- On short runs, migration is capped by
short_task_max_migrations
Common Pitfalls
- Uniform islands (strength too low) → little diversity benefit; raise
island_strategy_strength - Migration too aggressive → premature convergence; rely on adaptive stagnation gating
- Exploration island flooding → tune
exploration_restart_ratioand novelty ratio - Short runs over-migrating → keep
short_task_max_migrationslow (default 1)
4. Acceptance Criteria
- Islands occupy distinct points on the exploration↔exploitation spectrum
- Migration triggers only after stagnation (adaptive, not periodic-only)
- Novelty survivors maintain inter-island diversity
- Short runs respect the migration cap
- Final best beats a uniform IslandGA baseline on the same problem