Beyond Monte Carlo Tree Search: Implicit Chess Strategies with Discrete Diffusion

Challenges of Large Language Models in Complex Problem-Solving

Large language models (LLMs) generate text in a step-by-step manner, which limits their ability to handle tasks that require multiple reasoning steps, such as structured writing and problem-solving. This limitation affects their coherence and decision-making in complex scenarios. While some approaches evaluate various alternatives to improve prediction accuracy, they incur higher computational costs and can lead to errors if future forecasts are incorrect.

Limitations of Current Search Algorithms

Common search algorithms like Monte Carlo Tree Search (MCTS) and beam search are popular in AI planning and decision-making but come with significant limitations. These algorithms rely on repeated simulations of future scenarios, which increases computational costs and makes them unsuitable for real-time applications. Additionally, they depend on a value model to estimate each state; if this model is incorrect, it propagates errors throughout the search process. This accumulation of errors can severely impact decision-making accuracy, particularly in complex tasks requiring long-term planning.

Introducing DIFFUSEARCH: A New Framework for Decision-Making

To address these challenges, researchers from The University of Hong Kong, Shanghai Jiaotong University, Huawei Noah’s Ark Lab, and Shanghai AI Laboratory proposed DIFFUSEARCH. This innovative framework eliminates the need for explicit search algorithms like MCTS. Instead, DIFFUSEARCH trains a policy to directly predict and utilize future representations, refining these predictions iteratively through diffusion models. By integrating the world model and policy into a single framework, DIFFUSEARCH reduces computational overhead while enhancing efficiency and accuracy in long-term planning.

Training Methodology

The DIFFUSEARCH framework employs supervised learning, using Stockfish as an oracle to label board states from chess games. It explores different future representations, ultimately selecting the action-state (s-asa) method for its simplicity and efficiency. Rather than predicting future sequences directly, the model employs discrete diffusion modeling, utilizing self-attention and iterative denoising to gradually enhance action predictions. This approach avoids the costly marginalization of future states during inference by sampling directly from the trained model. An easy-first decoding strategy prioritizes more predictable tokens for denoising, thus improving accuracy.

Performance Evaluation

Researchers evaluated DIFFUSEARCH against three transformer-based baselines: State-Action (S-A), State-Value (S-V), and Action-Value (SA-V) models. Using a dataset of 100,000 chess games, they implemented GPT-2-based models with specific configurations and conducted evaluations on action accuracy, puzzle accuracy, and Elo ratings from a 6000-game internal tournament. DIFFUSEARCH outperformed S-A by 653 Elo points and showed a 19% improvement in action accuracy while using significantly fewer data records than SA-V. The discrete diffusion with linear λt achieved the highest accuracy of 41.31%, surpassing autoregressive and Gaussian methods.

Conclusion and Future Applications

The proposed model demonstrates that implicit search through discrete diffusion can effectively replace explicit search methods and enhance decision-making in chess. Despite using an external oracle and a limited dataset, it shows promise for improvement through self-play and long-context modeling. This method can also be applied to enhance next-token prediction in language models, serving as a foundation for further exploration in AI planning and decision-making.

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