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In the context of the Classification and Regression Trees (CART) algorithm, the efficient splitting of categorical features using standard criteria like GINI and Entropy is well-established. However, using the Mean Absolute Error (MAE) criterion for categorical features has traditionally relied on various numerical encoding methods. This paper demonstrates that unsupervised numerical encoding methods are not viable for MAE criteria. Furthermore, we present a novel and efficient splitting algorithm that addresses the challenges of handling categorical features with the MAE criterion. Our findings underscore the limitations of existing approaches and offer a promising solution to enhance the handling of categorical data in CART algorithms.

AAAI 2026 Main Conference

Binary Split Categorical Feature with Mean Absolute Error Criteria in CART

technical paper

We are pleased to announce the Fortieth AAAI Conference on Artificial Intelligence (AAAI-26), which will be held in Singapore EXPO from January 20 to January 27, 2026.

The purpose of the AAAI conference series is to promote research in Artificial Intelligence (AI) and foster scientific exchange between researchers, practitioners, scientists, students, and engineers across the entirety of AI and its affiliated disciplines. AAAI-26 will feature technical paper presentations, special tracks, invited speakers, workshops, tutorials, poster sessions, senior member presentations, competitions, and exhibit programs, and a range of other activities to be announced.<br><br>

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We are pleased to announce the Fortieth AAAI Conference on Artificial Intelligence (AAAI-26), which will be held in Singapore EXPO from January 20 to January 27, 2026.

In this New Faculty Highlights, I begin with the reward free exploration that learns broad state and skill coverage with intrinsic rewards and remains robust under misspecification during efficient finetuning; guided generation methods that preserve the prior policy and mitigate reward hacking; and AI for science and healthcare, including practical RL for autonomous laboratories and automatic diagnosis. Building
on impacts evidenced by publications, adoption, and awards. My future work will pursue imitation learning and contextual multi task RL that connect behavioral cloning with interactive policies without explicit reward design; personalized and multi-tasked offline to online adaptation with in-context demonstrations. In parallel, I am broadening the impact of AI for science and healthcare through existing collaborations. I will close with a talk that surveys these results and outlines an agenda for reinforcement learning without explicit rewards.

Reinforcement Learning Without Explicit Rewards: Theory and Practice

Large Language Models show promise in emotion understanding, social reasoning, and empathy, yet they struggle with psychologically grounded tasks that require inferring implicit mental states in context-rich, ambiguous settings. These limitations arise from the absence of theory-aligned supervision and the difficulty of capturing nuanced mental processes in real-world narratives. To address this gap, we leverage expert-labeled, psychologically rich scenarios and propose a trajectory-aware reinforcement learning framework that explicitly imitates expert psychological thought patterns. By integrating real-world stimuli with structured reasoning guidance, our approach enables compact models to internalize social-cognitive principles, perform nuanced psychological inference, and support continual self-improvement. Comprehensive experiments across multiple benchmarks further demonstrate that our models achieve expert-level interpretive capabilities, exhibiting strong out-of-distribution generalization and robust continual learning across diverse, challenging, and psychologically grounded tasks.

From Stimuli to Minds: Enhancing Psychological Reasoning in LLMs via Bilateral Reinforcement Learning

Accurate detection of cancer tissue regions (CTR) enables deeper analysis of the tumor microenvironment and offers crucial insights into treatment response. Traditional CTR detection methods, which typically rely on the rich cellular morphology in histology images, are susceptible to a high rate of false positives due to morphological similarities across different tissue regions. The groundbreaking advances in spatial transcriptomics (ST) provide detailed cellular phenotypes and spatial localization information, offering new opportunities for more accurate cancer region detection. However, current methods are unable to effectively integrate histology images with ST data, especially in the context of cross-sample and cross-platform/batch settings for accomplishing the CTR detection. To address this challenge, we propose SpaCRD, a transfer learning-based method that deeply integrates histology images and ST data to enable reliable CTR detection across diverse samples, platforms, and batches. Once trained on source data, SpaCRD can be readily generalized to accurately detect cancerous regions across samples from different platforms and batches. The core of SpaCRD is a category-regularized variational reconstruction-guided bidirectional cross-attention fusion network, which enables the model to adaptively capture latent co-expression patterns between histological features and gene expression from multiple perspectives. Extensive benchmark analysis on 23 matched histology-ST datasets spanning various disease types, platforms, and batches demonstrates that SpaCRD consistently outperforms existing eight state-of-the-art methods in CTR detection. Code availability and reproducibility details are in the Supplementary Materials.

SpaCRD: Multimodal Deep Fusion of Histology and Spatial Transcriptomics for Cancer Region Detection

Accurately determining the shape of deformable objects and
the location of their internal structures is crucial for
medical tasks that require precise targeting, such as
robotic biopsies.
We introduce LUDO, a method for accurate low-latency
understanding of deformable objects.
LUDO reconstructs objects in their deformed state,
including their internal structures, from a single-view
point cloud observation in under 30 ms using occupancy
networks.
LUDO provides uncertainty estimates for its predictions.
Additionally, it provides explainability by highlighting
key features in its input observations.
Both uncertainty and explainability are important for
safety-critical applications such as surgery.
We evaluate LUDO in real-world robotic experiments,
achieving a success rate of 98.9% for puncturing various
regions of interest (ROIs) inside deformable objects.
We compare LUDO to a popular baseline and show its superior
ROI localization accuracy, training time, and memory
requirements.
LUDO demonstrates the potential to interact with deformable
objects without the need for deformable registration
methods.

LUDO: Low-latency understanding of deformable objects using
point cloud occupancy functions

The rapid advancements in artificial intelligence (AI) have primarily focused on the process of learning from data to acquire knowledgeable learning systems. As these systems are increasingly deployed in critical areas, ensuring their privacy and alignment with human values is paramount. Recently, selective forgetting (also known as machine unlearning) has shown promise for privacy and data removal tasks, and has emerged as a transformative paradigm shift in the field of AI. It refers to the ability of a model to selectively erase the influence of previously seen data, which is especially important for compliance with modern data protection regulations and for aligning models with human values. Despite its promise, selective forgetting raises significant privacy concerns, especially when the data involved come from sensitive domains. While new unlearning-induced privacy attacks are continuously proposed, each is shown to outperform its predecessors using different experimental settings, which can lead to overly optimistic and potentially unfair assessments that may disproportionately favor one particular attack over the others. In this work, we present the first comprehensive benchmark for evaluating privacy vulnerabilities in selective forgetting. We extensively investigate privacy vulnerabilities of machine unlearning techniques and benchmark privacy leakage across a wide range of victim data, state-of-the-art unlearning privacy attacks, unlearning methods, and model architectures. We systematically evaluate and identify critical factors related to unlearning-induced privacy leakage. With our organized codebase and novel insights, we aim to provide a standardized tool for practitioners seeking to deploy customized unlearning applications with faithful privacy assessments.

Towards Benchmarking Privacy Vulnerabilities in Selective Forgetting with Large Language Models

Novel object synthesis by integrating distinct textual concepts from diverse categories remains a significant challenge in Text-to-Image (T2I) generation. Existing methods often suffer from insufficient concept mixing, lack of rigorous evaluation, and suboptimal outputs—manifesting as conceptual imbalance, superficial combinations, or mere juxtapositions. To address these limitations, we propose \textbf{Reinforcement Mixing Learning (RMLer)}, a framework that formulates cross-category concept fusion as a reinforcement learning problem: mixed features serve as states, mixing strategies as actions, and visual outcomes as rewards. Specifically, we design an MLP-policy network to predict dynamic coefficients for blending cross-category text embeddings. We further introduce visual rewards based on (1) semantic similarity and (2) compositional balance between the fused object and its constituent concepts, optimizing the policy via proximal policy optimization. At inference, a selection strategy leverages these rewards to curate the highest-quality fused objects. Extensive experiments demonstrate RMLer’s superiority in synthesizing coherent, high-fidelity objects from diverse categories, outperforming existing methods. Our work provides a robust framework for generating novel visual concepts, with promising applications in film, gaming, and design.

RMLer: Synthesizing Novel Objects Across Diverse Categories via Reinforcement Mixing Learning

Sketch person re-identification aims to match hand-drawn sketches with RGB surveillance images, yet remains challenging due to severe modality discrepancies and limited labeled data. To address this, we propose KTCAA, a theoretically grounded and interpretable framework for few-shot cross-modal transfer learning. From the perspective of generalization bounds, we identify two key controllable factors essential to minimizing target domain error: (1) domain discrepancy, which reflects the difficulty of aligning source and target distributions in the feature space; and (2) perturbation invariance, which measures the model’s robustness to cross-modal variations. To address these challenges, we design two corresponding modules: (1) Alignment Augmentation (AA), which applies localized sketch-style transformations to simulate target modality distributions, introducing slight but meaningful feature shifts that guide gradual distribution alignment during training; and (2) Knowledge Transfer Catalyst (KTC), which enhances perturbation invariance by generating worst-case adversarial modality perturbations and enforcing output consistency under such perturbations. These modules are jointly optimized within a meta-learning framework that transfers alignment knowledge from RGB-rich domains to sketch scenarios. Experiments on multiple benchmarks demonstrate that KTCAA achieves state-of-the-art performance, particularly under limited data and cross-domain transfer settings.

A Theory-Inspired Framework for Few-Shot Cross-Modal Sketch Person Re-Identification

The Aperiodic Tiling Complements Problem (ATCP) involves finding the full set of possible aperiodic complements of a given pattern.
This has become a classic problem in music theory, with some recent attempts to model it using Integer Linear Programming (ILP) and Boolean Satisfiability (SAT) frameworks.
In this paper, we propose and compare different models of ATCP encoded in Constraint Programming (CP).
The most effective approach admits two phases: a first one that allows us to merge (join) several subsets of linear constraints under the form of tables with large arity, and a second one that advantageously exploits the generated tables to discard periodic tiling complements.
Our experimental results show that our approach significantly outperforms the state-of-the-art, solving every instance of a classical benchmark (standard Vuza rhythms for canons
with period set to 420 and 900) in a time within 5 seconds to 2 minutes (except the largest instance being solved in 18 minutes).

Aperiodic Tiling and Rhythmic Canons: A CP Journey

Recommendation systems commonly face selection bias from missing-not-at-random (MNAR) data. While propensity-based methods such as inverse propensity scoring (IPS) and doubly robust (DR) estimators are widely used, their existing variant methods typically optimize only one or two evaluation criteria, neglecting their interdependencies and inherent trade-offs, limiting robustness.
To address this, we propose a bin-based \textbf{Unified Propensity Optimization (UPO)} framework that integrates and upper-bounds four widely-used criteria by revealing a fundamental structural commonality among their corresponding metrics, Expected Calibration Error (calibration), Bias Minimizing Squared Error (feature balancing), DR bias, and DR variance, showing that each metric can be represented as a feature- and model-driven adaptive weights multiplied by propensity estimation errors. Based on this unified structure, we design a minimax optimization algorithm employing adversarial weighting well addressing the trade-off between all four criteria . Theoretically, we demonstrate that minimizing the UPO loss effectively controls the original global-scale metrics, ensuring their simultaneous improvements without incurring additional bias, and achieving reduced variance compared to naïvely adding up multiple penalization terms.
Empirically, experiments on semi-synthetic and real-world datasets validate UPO’s efficacy, demonstrating superior performance compared to state-of-the-art methods with minor computational overhead.

Unified Minimax Optimization Framework for Propensity Score Estimation in Debiased Recommendation

Modern task-oriented dialogue (TOD) systems increasingly rely on large language model (LLM) agents, leveraging Retrieval-Augmented Generation (RAG) and long-context capabilities for long-term memory utilization. However, these methods are primarily based on semantic similarity, overlooking task intent and reducing task coherence in multi-session dialogues. To address this challenge, we introduce **MemGuide**, a two-stage framework for intent-driven memory selection. (1) **Intent‑Aligned Retrieval** matches the current dialogue context with stored intent descriptions in the memory bank, retrieving QA‑formatted memory units that share the same goal. (2) **Missing‑Slot Guided Filtering** employs a chain‑of‑thought slot reasoner to enumerate unfilled slots, then uses a fine‑tuned LLaMA‑8B filter to re‑rank the retrieved units by marginal slot‑completion gain. The resulting memory units inform a proactive strategy that minimizes conversational turns by directly addressing information gaps. Based on this framework, we introduce the **MS-TOD**, the first multi-session TOD benchmark comprising 132 diverse personas, 956 task goals, and annotated intent-aligned memory targets, supporting efficient multi‑session task completion. Evaluations on MS-TOD show that MemGuide raises the task success rate by 11\% (88\%→99\%) and reduces dialogue length by 2.84 turns in multi-session settings, and maintains parity with single‑session benchmarks.

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Reinforcement Learning Without Explicit Rewards: Theory and Practice

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PRESENTATIONS

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RESOURCES

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