ATLAS: Scaffold-Free Algorithm Synthesis by LLMs via Embedding-Guided Quality-Diversity Search
Organizations: School of Computing Technologies, RMIT University, Melbourne, VIC, Australia · School of Computing and Leeds University Business School, University of Leeds, Leeds, UK · La Trobe Business School, La Trobe University, Melbourne, VIC, Australia · Effective AI, Melbourne, VIC, Australia
Abstract
Most LLM-based automated algorithm design methods optimize a designated component within a human-specified scaffold, fixing overall organization and component interactions. We present ATLAS, an embedding-guided quality-diversity framework for scaffold-free full-algorithm synthesis in combinatorial optimization. The problem specification supplies objectives and constraints; a minimal I/O interface fixes only instance and solution formats; the LLM chooses and restructures components, interactions, and control flow. This freedom enlarges the search space, risking invalid candidates and premature convergence to one design region. ATLAS independently detects execution, interface, and feasibility failures, recomputes objectives, and applies error-conditioned repair; similarity-based archive management preserves algorithms across embedding-space regions to counter premature convergence. Its three-layer search refines the best design, gives other regions dedicated refinement opportunities, and performs cross-region synthesis to recombine components and their interactions. Across four NP-hard problems, ATLAS outperforms several state-of-the-art component-synthesis methods and a matched full-synthesis baseline while remaining competitive with strong human-designed algorithms. One ATLAS run retains several algorithms with comparable performance from distinct embedding-space regions rather than a single design. Code inspection finds that these multi-component designs differ in their primary construction or global-search backbone. Our results suggest that embedding-guided quality-diversity search can make the enlarged full-algorithm design space practically searchable. Source code and exact executable prompts are available at https://github.com/Danial-Yazdani/ATLAS .
Figures & tables
| Parameter | Value | Parameter | Value |
| Archive capacity | Layer 1 size | ||
| Initialization | 50 algorithms | Clustering | K-Medoids, adaptive |
| Multi-ref operators (refs) | Single-ref operator probs | ||
| Combine | Improve , Tune | ||
| Diverge | Simplify | ||
| Embedding model | mGTE-large-en-v1.5 [ 58 ] | LLM | GPT-5-mini (T=1.0, LOW) |
| Group | Method | FSS | CVRP | CVRPTW | QAP |
|---|---|---|---|---|---|
| Domain-specific | NEH | 2.809% | – | – | – |
| IG-TB (Taillard acc.) | 0.000% | – | – | – | |
| Iterative Beam Search | 1.787% | – | – | – | |
| OR-Tools (GLS) | – | 1.430% | 0.121% | – | |
| PyVRP (ILS) | – | 0.000% | 0.000% | – | |
| VROOM | – | 0.095% | 0.060% | – |
| Group | Method | FSS | FSS | CVRP | CVRP |
|---|---|---|---|---|---|
| Domain-specific | NEH | 1.143% | 4.133% | – | – |
| IG-TB (Taillard acc.) | 0.000% | 0.000% | – | – | |
| Iterative Beam Search | 2.321% | 2.865% | – | – | |
| OR-Tools (GLS) | – | – | 0.162% | 4.930% | |
| PyVRP (ILS) | – | – | 0.000% | 0.000% | |
| VROOM | – | – | 0.000% | 0.975% |
| Problem | Training-selected representatives, ordered by descriptive test gap |
|---|---|
| FSS | Priority-Seeded Prefix-Guided LNS with Lightweight Anneal (0.331%); Priority-seeded NEH with Guided Neighborhood Search (0.458%); Priority-Spectral Hybrid with Tabu-Repair Local Search (0.472%); Prefix-Aware Hybrid Genetic with Annealed Polish (0.478%); Sampled Pairwise Greedy with Bounded Cache and Adaptive Iterated Refinement (0.527%); Hybrid NEH-Regret Genetic Search with Aggressive Complexity Reduction (0.714%); Guided Greedy Adaptive Cache with Pheromone and Block Relocation (0.965%); Bottleneck-Guided Greedy with ILS and Simulated Annealing (1.239%) |
| CVRP | Hybrid Multi-Start Clustered-Repair Large Neighborhood Search (0.000%); Multi-Start Regret Insertion with Focused Large Neighborhood Search (0.095%); Spectral-Seeding Regret-LNS with Focused Savings (0.191%); Hybrid Demand-Seeding with Localized Destroy-and-Repair (3.622%); Clustered Demand-Aware Insertion with Focused LNS (3.622%); Adaptive Clustered Chain-Savings Solver (3.908%) |
| CVRPTW | Large-Neighborhood Search with Time-Aware Regret Repair (0.000%); Ruin-and-Recreate Vehicle Routing with Time Windows (0.000%); Hybrid Label-Constructive and Ruin-Repair Routing (0.000%); Hybrid Adaptive Ruin-and-Repair with Temporal Beam Seeding (0.060%); Hybrid Guided Repair with Selective Savings Merge (0.302%); Permutation-Guided Large Neighborhood Search (2.171%); Radial and Time-Priority Insertion with Neighbor Guidance (3.317%) |
| QAP | Hierarchical Spectral-Memetic Solver with Block Neighborhoods and Cycle Diversification (0.440%); Soft-Probabilistic Beam with Block Reassignment and Tabu Polishing (0.461%); Adaptive Spectral-Pheromone Memetic Solver (0.496%); Spectral-Guided Adaptive Large-Neighborhood Search with Local Intensification (0.525%); Spectral-Softassign Hybrid with Mixed Local Search (0.813%) |
| Configuration | CVRP gap (%) | FSS gap (%) |
|---|---|---|
| Variant A: All layers | 0.094 | 0.347 |
| Variant B: Layer 1 only | 3.620 | 0.814 |
| Variant C: Layers 2+3 | 0.668 | 0.474 |
| Variant D: Layer 3 only | 2.095 | 0.672 |
Appendix figures & tables14 assets
Supplementary material from the paper’s appendix.
Appendix
| Method | Scope | Primary Mechanism | Organizing Space | Preservation Logic |
|---|---|---|---|---|
| Component-Based Single-Algorithm Synthesis (Appendix A-B1 ) | ||||
| FunSearch [ 36 ] | Component | Islands + best-shot prompting | Output signatures (eval scores) | Cluster-biased sampling + island resets |
| EoH [ 25 ] | Component | Operator-based evolution | Fitness (scalar performance) | Fitness-based selection; no explicit diversity objective |
| ReEvo [ 57 ] | Component | Verbal gradients + reflection | Fitness + meta-objective constraints | Successful candidates under meta-objective constraints |
| HSEvo [ 9 ] | Component | Harmony Search + reflection | Embeddings (diversity indices) + fitness | Embedding diversity indices (SWDI/CDI) modulate search |
| MCTS-AHD [ 61 ] | Component | MCTS with LLM actions | Genealogy (tree) + UCT scores | Tree retention with UCT-based revisiting |
| Problem setting | Reference method | Raw mean objective |
|---|---|---|
| FSS | IG-TB (Taillard acc.) [ 38 , 45 , 12 ] | 3 343.00 |
| CVRP | PyVRP (ILS) [ 52 , 53 ] | 10.49 |
| CVRPTW | PyVRP (ILS) [ 52 , 53 ] | 16.58 |
| QAP | BMA [ 2 ] | 5 704 446 |
| FSS | IG-TB (Taillard acc.) [ 38 , 45 , 12 ] | 1 599.84 |
| FSS | IG-TB (Taillard acc.) [ 38 , 45 , 12 ] | 6 808.45 |
| CVRP gap (%) | FSS gap (%) | |||||
| 2 | 3 | 4 | 2 | 3 | 4 | |
| Relative mean gap (%) | 0.572 | 0.094 | 0.095 | 0.401 | 0.347 | 0.351 |
| Order | Class | Identifying evidence | Correction objective |
|---|---|---|---|
| 1 | Memory limit | Memory-limit flag or MemoryError | Reduce large materialized structures, unbounded containers, redundant copies, or deep recursion |
| 2 | Partial failure | Some training instances succeed and others fail | Preserve the core approach while handling edge cases and removing instance-dependent failures |
| 3 | Timeout | Timeout marker in the aggregate error | Reduce computational complexity, redundant work, and excessive iteration within the existing approach |
| 4 | Constraint violation | A feasibility keyword in the evaluator message (Table B.4 ) | Correct construction or modification logic so returned solutions satisfy the problem constraints |
| 5 | Runtime error | Exception, error, or traceback markers after excluding earlier classes | Locate and correct the source-level crash and add relevant defensive checks |
| 6 | Framework violation | Remaining unmatched validation or interface failure | Correct the entry point, signature, return type, output structure, or other interface requirement |
| Category | Keywords |
|---|---|
| Capacity and resources | exceeds capacity; capacity constraint; over capacity |
| Completeness | not all customers visited; missing jobs; missing items; missing customers |
| Uniqueness | visited multiple times; duplicate; appears multiple times |
| Permutation and sequence | not a valid permutation; job sequence length; invalid permutation; sequence length |
| General validity | constraint violation; invalid solution; feasibility; infeasible; out of range; invalid index; invalid customer; invalid item |
| Model | Access | Params | Dim. | Context |
| General-Purpose Models | ||||
| text-embedding-3-large (OpenAI) [ 34 ] | Proprietary | – | 3072 | 8K |
| text-embedding-3-small (OpenAI) [ 34 ] | Proprietary | – | 1536 | 8K |
| Qwen3-Embedding-0.6B [ 60 ] | Open | 0.6B | 1024 | 32K |
| Qwen3-Embedding-4B [ 60 ] | Open | 4.0B | 2560 | 32K |
| mGTE-large-en-v1.5 [ 58 ] | Open | 434M | 1024 | 8K |
| Text-Only | Code-Only | Concatenation (Early Fusion) | ||||
| Model Architecture | NNA (%) | CCI | NNA (%) | CCI | NNA (%) | CCI |
| General-Purpose Models | ||||||
| text-embedding-3-small (OpenAI) | 94.62 | 0.40 | 73.32 | 0.23 | 91.33 | 0.32 |
| text-embedding-3-large (OpenAI) | 91.44 | 0.35 | 65.38 | 0.14 | 86.62 | 0.25 |
| Qwen3-Embedding-0.6B | 88.77 | 0.29 | 75.81 | 0.22 | 91.80 | 0.31 |
| Qwen3-Embedding-4B | 89.53 | 0.29 | 77.09 | 0.21 | 95.33 | 0.39 |
| Persona Name | Persona Text |
|---|---|
| default | You are an expert computer scientist specializing in algorithm design for combinatorial optimization problems. |
| Single-Dimension Personas | |
| simplicity_focused | You are an algorithm designer who prioritizes elegant, minimal solutions. |
| complexity_embracing | You are an algorithm designer who builds sophisticated, feature-rich solutions. |
| modernist | You are an algorithm designer who uses cutting-edge techniques and recent innovations. |
| traditionalist | You are an algorithm designer who relies on proven, standard approaches. |
| Baseline | +Random Persona | +Divergence (ATLAS) | |||||||
| Model | Valid | MNND | MPD | Valid | MNND | MPD | Valid | MNND | MPD |
| CVRP | |||||||||
| GPT-4.1-Mini | 0.96 | 0.015 | 0.035 | 0.98 | 0.023 | 0.045 | 0.93 | 0.058 | 0.151 |
| GPT-5-mini (low) | 0.99 | 0.037 | 0.103 | 0.98 | 0.034 | 0.097 | 0.98 | 0.062 | 0.159 |
| Claude Haiku 4.5 | 0.86 | 0.029 | 0.077 | 0.89 | 0.027 | 0.068 | 0.90 | 0.064 | 0.147 |
| Llama 4 Maverick | 0.85 | 0.020 | 0.095 | 0.87 | 0.019 | 0.094 | 0.84 | 0.039 | 0.123 |
| Guidance Strategy | CVRP gap (%) | FSS gap (%) |
|---|---|---|
| Variant A: Semantic Guidance | 0.570 | 0.391 |
| Variant B: Fitness-Based Guidance | 2.601 | 0.715 |
| Variant C: Random Guidance | 3.143 | 0.884 |
| Reasoning effort | Relative mean gap (%) | Total tokens per run (k) | ||
|---|---|---|---|---|
| CVRP | FSS | CVRP | FSS | |
| Minimal | 1.815 | 0.597 | 6 146 (135) | 4 258 (178) |
| Low (default) | 0.094 | 0.347 | 6 335 (144) | 4 491 (246) |
| Medium | 0.092 | 0.301 | 8 126 (161) | 5 865 (272) |
| High | 0.000 | 0.292 | 10 928 (241) | 8 247 (294) |
| Underlying LLM | FSS gap (%) |
|---|---|
| GPT-5-nano (low) | 0.557 |
| GPT-5-mini (low) | 0.347 |
| GPT-5 (low) | 0.284 |
| Claude Haiku 4.5 (default) | 0.540 |
| LLM | Training-selected representatives, ordered by descriptive test gap |
|---|---|
| GPT-5-nano (low) | Permutation Based Flow Shop Heuristic with Cascaded Insertion and Local Search (0.474%); Hybrid Seeded Cascaded Insertion with Global Lookahead (0.501%); Fixed Permutation Flow Shop Seeded Local Search (0.527%); Diversified Guided Cascaded Beam Search for Permutation Flow Shop (0.753%); Hybrid Prefix Guided Insertion with Global Lookahead and Prefix Preserving Local Search (1.333%); Genetic Algorithm based on permutation population with crossover and mutation (1.372%); Greedy NEH-inspired permutation for flow shop makespan minimization (2.809%); Recursive Skyline Block Sequencing (3.319%); Hybrid Pheromone Guided Time Slice Sequencing (3.383%); Pheromone Guided Permutation Flow Shop Scheduler (3.483%) |
| GPT-5-mini (low) | Priority-Seeded Prefix-Guided LNS with Lightweight Anneal (0.331%); Priority-seeded NEH with Guided Neighborhood Search (0.458%); Priority-Spectral Hybrid with Tabu-Repair Local Search (0.472%); Prefix-Aware Hybrid Genetic with Annealed Polish (0.478%); Sampled Pairwise Greedy with Bounded Cache and Adaptive Iterated Refinement (0.527%); Hybrid NEH-Regret Genetic Search with Aggressive Complexity Reduction (0.714%); Guided Greedy Adaptive Cache with Pheromone and Block Relocation (0.965%); Bottleneck-Guided Greedy with ILS and Simulated Annealing (1.239%) |
| GPT-5 (low) | Pairwise backbone scheduling with regret beam construction and consensus edge relinking (0.277%); Precedence corridor scheduling with shockwave rebuild and edge voted relinking (0.280%); Vote guided anchor beam scheduling with cached insertion scoring and focused reconstruction (0.304%); Multi-sequence NEH flow shop heuristic with CDS, Palmer, and elite reinsertion search (0.391%); Consensus rollout scheduling with hot segment repair and block guided relinking (0.454%); Pairwise precedence learning with exact insertion and conflict focused segment reconstruction (0.460%); Tournament backbone search with window dynamic programming (0.800%); Cross-entropy random-key optimization with block permutation polishing (2.746%) |
| Claude Haiku 4.5 | Hybrid Adaptive Simulated Annealing with Dynamic Critical Path Guidance (0.484%); Simulated Annealing with Critical Path Optimization for Flow Shop Scheduling (0.571%); Simulated Annealing with Greedy Initialization for Flow Shop Scheduling (0.579%); Hybrid Memetic Algorithm with Adaptive Dual-Strategy Exploration (0.809%); Hybrid Adaptive Metaheuristic with Critical Path Learning (1.016%); Hybrid Initialization and Local Search for Flow Shop Scheduling (1.237%); Hybrid Memetic Strategy with Dual-Phase Evolution and Adaptive Intensity Balancing (1.537%); Genetic Algorithm with Dual Crossover Operators and Adaptive Multi-Strategy Mutations (1.558%); Constraint-Based Graph Routing with Bottleneck-Aware Optimization (2.181%) |
Automated Algorithm Discovery
Automated algorithm discovery develops methods that generate and test executable algorithms for optimization, science, software, and machine learning.
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