Automatic Goal Discovery in Subgoal Monte Carlo Tree Search

Monte Carlo Tree Search (MCTS) is a heuristic search algorithm that can play a wide range of games without requiring any domain-specific knowledge. However, MCTS tends to struggle in very complicated games due to an exponentially increasing branching factor. A promising solution for this problem is to focus the search only on a small fraction of states. Subgoal Monte Carlo Tree Search (S-MCTS) achieves this by using a predefined subgoal-predicate that detects promising states called subgoals. However, not only does this make S-MCTS domaindependent, but also it is often difficult to define a good predicate. In this paper, we propose using quality diversity (QD) algorithms to detect subgoals in real-time. Furthermore, we show how integrating QD-algorithms into S-MCTS significantly improves its performance in the Physical Travelling Salesmen Problem without requiring any domain-specific knowledge

MCTS-Minimax Hybrids with State Evaluations

Monte-Carlo Tree Search (MCTS) has been found to show weaker play than minimax-based search in some tactical game domains. This is partly due to its highly selective search and averaging value backups, which make it susceptible to traps. In order to combine the strategic strength of MCTS and the tactical strength of minimax, MCTS-minimax hybrids have been introduced, embedding shallow minimax searches into the MCTS framework. Their results have been promising even without making use of domain knowledge such as heuristic evaluation functions. This article continues this line of research for the case where evaluation functions are available. Three different approaches are considered, employing minimax with an evaluation function in the rollout phase of MCTS, as a replacement for the rollout phase, and as a node prior to bias move selection. The latter two approaches are newly proposed. Furthermore, all three hybrids are enhanced with the help of move ordering and k-best prunin! g for minimax. Results show that the use of enhanced minimax for computing node priors results in the strongest MCTS-minimax hybrid investigated in the three test domains of Othello, Breakthrough, and Catch the Lion. This hybrid, called MCTS-IP-M-k, also outperforms enhanced minimax as a standalone player in Breakthrough, demonstrating that at least in this domain, MCTS and minimax can be combined to an algorithm stronger than its parts. Using enhanced minimax for computing node priors is therefore a promising new technique for integrating domain knowledge into an MCTS framework

Linguistic Summaries as Explanation Mechanism for Classification Problems

The amount and complexity of generated and collected data is rapidly growing. As a consequence, it is increasingly hard to understand the data and extract useful information. Transparency, interpretability and understandability contribute towards explainability of the data, which is crucial for the user for both efficient and effective usage of it and trust in these data-based decisions. In this paper, we investigate how linguistic summaries can serve as an explanation mechanism for classification results. Linguistic summaries are template-based, semi-natural language-like sentences that can verbalize these (classification) patterns. We develop linguistic summarizations for the classification results of two publicly available data sets and perform an initial evaluation with a small group of potential users. The preliminary results look promising

On-Line Parameter Tuning for Monte-Carlo Tree Search in General Game Playing

Many enhancements have been proposed for Monte-Carlo Tree Search (MCTS). Some of them have been applied successfully in the context of General Game Playing (GGP). MCTS and its enhancements are usually controlled by multiple parameters that require extensive and time-consuming computation to be tuned in advance. Moreover, in GGP optimal parameter values may vary depending on the considered game. This paper proposes a method to automatically tune search-control parameters on-line for GGP. This method considers the tuning problem as a Combinatorial Multi-Armed Bandit (CMAB). Four strategies designed to deal with CMABs are evaluated for this particular problem. Experiments show that on-line tuning in GGP almost reaches the same performance as off-line tuning. It can be considered as a valid alternative for domains where off-line parameter tuning is costly or infeasible