arXiv Machine Learning

Is Monte Carlo Tree Search Just Every-Visit Monte Carlo Control?

The article argues that Monte Carlo Tree Search (MCTS) and every‑visit Monte Carlo (MC) control are essentially the same method, differing only in terminology and presentation. It shows that MCTS’s four stages—selection, expansion, simulation, and backup—can be reduced to two core operations: sampling trajectories under the current policy and performing every‑visit MC updates. The note aims to make this equivalence explicit and easier to recognize.

arXiv AI
Sep 17

Online Robust Reinforcement Learning Through Monte-Carlo Planning

The paper introduces a robust variant of Monte Carlo Tree Search that addresses ambiguities in transition dynamics and reward distributions, bridging the gap between simulation-based planning and real-world deployment. It incorporates a robust power mean backup operator and exploration bonuses to guarantee finite-sample convergence at every node, achieving an ≠O(n−1/2) convergence rate for root value estimation comparable to standard MCTS. Empirical results demonstrate robust performance in planning tasks even under significant model mismatches.

By Tuan Dam, Kishan Panaganti, Brahim Driss, Adam Wierman
arXiv AI
Jul 20

Process Reward Informed Tree Rollout for Effective Multi-Turn RL

arXiv:2607. 15610v1 Announce Type: cross Abstract: Reinforcement learning (RL) has become a key approach for training LLM agents, yet popular methods such as GRPO/RLOO rely on multiple independently sampled complete trajectories for advantage estimation.

By Xintong Li, Sha Li, Yuwei Zhang, Changlong Yu, Rongmei Lin, Hongye Jin, Shuyi Guan, Xin Liu, Linwei Li, Qingyu Yin, Jingbo Shang
arXiv Computation and Language
Oct 1

OPTS-TTPO: Enhancing Finite-Sample Policy-Gradient Learning with Tree Search

arXiv:2609.40035v1 Announce Type: new Abstract: The policy-gradient theorem gives the exact gradient under the current policy, but finite on-policy samples may miss rare high-return trajectories. We...

By Junyu Lu, Shichao Weng, Zhiqiang Wang, Haojie Luo, Jingfan Zhang, Yuhua Zhou, Cheng Du, Yuzhuo Zhang, Xi Li, Jinwei Du, Tiancheng Feng, Chuan Xiao, Shuyuan Zheng
arXiv Machine Learning
Sep 10

PMCTS: Principled Parallelized Inference Time Scaling with Particle Monte Carlo Tree Search

The paper introduces Particle MCTS (PMCTS), a parallelized version of Monte Carlo Tree Search designed for GPU acceleration and batch-parallel neural network evaluations. PMCTS preserves policy improvement guarantees of modern MCTS algorithms while scaling efficiently with parallel compute. Empirical results show that PMCTS consistently outperforms or matches heuristic-based baselines across various MCTS and reinforcement learning domains, including chess, Go, and both discrete and continuous control benchmarks.

By Yaniv Oren, Viliam Vadocz, Joery A. de Vries, Wendelin B\"ohmer, Matthijs T. J. Spaan, Hendrik Baier
arXiv AI
Sep 3

DiffuSearch: How Hybrid Trajectory Planning Benefits from Aligned Objectives in Diffusion and Action Space

DiffuSearch is a hybrid trajectory planner for autonomous driving that unifies objectives across both generation and refinement stages. It first uses a guided diffusion model to produce scene-consistent joint trajectories, then refines them with a Monte Carlo Tree Search that shares the same driving goals—collision avoidance, drivable area compliance, comfort, and progress. Experiments on nuPlan and interPlan benchmarks show that this synergy reduces collisions and improves comfort, especially in complex interactive scenarios.

By Steffen Hagedorn, Aron Distelzweig, Alexandru P. Condurache
arXiv Machine Learning
Sep 21

GEM-MPC: Balancing Exploration and Exploitation through Expert-Guided Planning

GEM-MPC is a reinforcement learning method that blends MPPI planning with policy learning to balance exploration and exploitation in high-dimensional continuous control tasks. It trains a policy to clone the planner while also maintaining a KL-regularized policy that explores around the planner’s suggestions, thereby improving the synergy between planning and learning. The approach introduces Gated Prior Distillation, which selectively updates policies from stored planning distributions only when they offer better targets, reducing the influence of stale data without costly reanalysis. Across continuous-control benchmarks, GEM-MPC outperforms existing planning-based baselines while using lower computational budgets.

By Alvaro Serra-Gomez, Thomas Moerland
arXiv AI
Oct 15

Belief Embedding Tree Search

arXiv:2610.15046v1 Announce Type: new Abstract: Beliefs in a Partially Observable Markov Decision Process (POMDP) are posterior distributions over the hidden state given the agent's history of action...

By Christopher Solinas, Radovan Halu\v{s}ka, Martin Schmid, Michael Buro, Nathan R. Sturtevant, Michael Bowling