Game Solving with Online Fine-Tuning

Ti-Rong Wu,¹ Hung Guei,¹ Ting Han Wei,² Chung-Chin Shih,^1,3 Jui-Te Chin,³ I-Chen Wu^1,3

¹ Academia Sinica, ² University of Alberta, ³ National Yang Ming Chiao Tung University

NeurIPS 2023

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Abstract

Game solving is a similar, yet more difficult task than mastering a game. Solving a game typically means to find the game-theoretic value (outcome given optimal play), and optionally a full strategy to follow in order to achieve that outcome. The AlphaZero algorithm has demonstrated super-human level play, and its powerful policy and value predictions have also served as heuristics in game solving. However, to solve a game and obtain a full strategy, a winning response must be found for all possible moves by the losing player. This includes very poor lines of play from the losing side, for which the AlphaZero self-play process will not encounter. AlphaZero-based heuristics can be highly inaccurate when evaluating these out-of-distribution positions, which occur throughout the entire search. To address this issue, this paper investigates applying online fine-tuning while searching and proposes two methods to learn tailor-designed heuristics for game solving. Our experiments show that using online fine-tuning can solve a series of challenging 7x7 Killall-Go problems, using only 23.54% of computation time compared to the baseline without online fine-tuning. Results suggest that the savings scale with problem size. Our method can further be extended to any tree search algorithm for problem solving. Our code is available at https://rlg.iis.sinica.edu.tw/papers/neurips2023-online-fine-tuning-solver.

Online Fine-Tuning Solver

The proposed online fine-tuning game solver comprises a manager, a set of workers, and an online fine-tuning trainer.

The manager maintains a search tree. During the proof search, the manager (1) employs a heuristic (i.e., an AlphaZero network model) to assign jobs to the workers to solve; (2) forwards solved positions or critical positions to the trainer to fine-tune.
The workers use the same heuristic as the manager, attempt to solve the jobs within given constraints, and then return the solutions.
The online fine-tuning trainer fine-tunes the heuristic using received positions, then updates the heuristic the manager and worker use.

In online fine-tuning, the manager forwards positions that require fine-tuning to the trainer.

Solved positions are positions where theoretic outcomes are found. The trainer explicitly guides the network model to learn their outcomes.
Critical positions are unsolved positions that the solver is currently focusing on solving. The trainer uses them as initial positions for self-play.

Experiment Results

We select a set of three-move openings based on expert recommendations. These openings can be classified into four groups, named after their commonly shared first move opening: Jump (J), Knight’s move (K), Diagonal jump (D), and Stretch (S).

Each opening is named according to its group and position; for instance, JA represents the position resulting from Black playing at A in the jump group.

Our experiments show that using online fine-tuning can solve a series of challenging 7x7 Killall-Go problems, using only 23.54% of computation time compared to the baseline without fine-tuning.

BASELINE: 1,021,692 seconds.
ONLINE-SP: 538,092 seconds.
ONLINE-CP: 240,556 seconds.
ONLINE-SP+CP: 255,359 seconds.