LLM-Guided Heuristic Design from Simulation Traces: A Case Study in Dynamic Production and AGV Scheduling
2026-08-10 • Artificial Intelligence
Artificial Intelligence
AI summaryⓘ
The authors created a method that uses large language models (LLMs) to improve policies in simulations by analyzing detailed event traces, not just overall scores. They run multiple simulations of a policy, then use the worst-performing run to identify problems and suggest code changes. This approach was tested in a factory scheduling simulation with automated guided vehicles and outperformed traditional methods. Their findings show that using detailed simulation data helps make smarter improvements to complex scheduling policies.
Simulation-based optimizationLarge language models (LLMs)Discrete-event simulationAutomated guided vehicles (AGVs)Heuristic designPolicy improvementSchedulingMetaheuristicsRolling-MILPCode-level revisions
Authors
Jinbo Li, Chuanhao Li
Abstract
Simulation-based optimization (SBO) evaluates executable policies under stochastic dynamics, but most methods treat the simulator as a black box: aggregate scores rank candidates without revealing why they fail or which policy logic should change. We present an LLM-guided heuristic design framework that uses repeated simulation for selection and event-level traces for diagnosis. Each incumbent is assessed through multiple replications, while replaying its lowest-scoring one produces a queryable trace. A manager agent formulates bottleneck hypotheses from this evidence, and editing agents implement parallel code-level revisions. After execution checks and repeated evaluation, best-so-far selection retains only improvements. LLM revision occurs between evaluation batches, while a fixed policy controls each simulation run. We evaluate the framework in a discrete-event simulation of dynamic production and automated guided vehicle (AGV) scheduling. Across five independent optimization runs with Gemini-3.1-Pro, final mean scores averaged 77.51 on the simulator's 0-100 scale. In the highest-scoring run, trace-based diagnoses motivated proactive charging, distance-aware AGV assignment, and rebalanced dispatch priorities, raising the best-so-far mean score from 62.49 to 78.61. On 100 matched seeds, the best final policy outscored representative rolling-MILP, rule-based, and metaheuristic policies on every seed and retained its advantage under random faults without re-optimization. After separate re-optimization for a longer horizon and variable order interarrival times, the resulting policies again outscored all baselines. Ablations with two LLM backbones showed that removing either parallel candidate generation or trace-database access reduced final mean scores. These results show that simulation traces can guide targeted code-level policy improvement in complex simulation-based scheduling.