Ning Wu

User-item interaction data in collaborative filtering and graph modeling tasks often exhibit power-law characteristics, which suggest the suitability of hyperbolic space modeling. Hyperbolic Graph Convolution Neural Networks (HGCNs) are a novel technique that leverages the advantages of GCN and hyperbolic space, and then achieves remarkable results. However, existing HGCN methods have several drawbacks: they fail to fully leverage hyperbolic space properties due to arbitrary embedding initialization and imprecise tangent space aggregation; they overlook auxiliary information that could enrich the collaborative graph; and their training convergence is slow due to margin ranking loss and random negative sampling. To overcome these challenges, we propose Hyperbolic Graph Collaborative for Heterogeneous Recommendation (HGCH), an enhanced HGCN-based model for collaborative filtering that integrates diverse side information into a heterogeneous collaborative graph and improves training convergence speed. HGCH first preserves the long-tailed nature of the graph by initializing node embeddings with power law prior; then it aggregates neighbors in hyperbolic space using the gyromidpoint method for accurate computation; finally, it fuses multiple embeddings from different hyperbolic spaces by the gate fusion with prior. Moreover, HGCH employs a hyperbolic user-specific negative sampling to speed up convergence. We evaluate HGCH on four real datasets, and the results show that HGCH achieves competitive results and outperforms leading baselines, including HGCNs. Extensive ablation studies further confirm its effectiveness.

Large Language Models (LLMs) have shown impressive performance in various domains, prompting researchers to explore their potential application in recommendation systems. However, directly applying LLMs to recommendation tasks has proven to be less effective due to the significant gap between the data used for pre-training LLMs and the specific requirements of recommendation tasks. In this study, we propose Direct Multi-Preference Optimization (DMPO), a streamlined framework to bridge this gap and enhance the alignment of LLMs for recommendation tasks. DMPO can be viewed as a pair-wise ranking loss to distinguish between positive and negative samples in recommendation tasks. Furthermore, DMPO improves the performance of LLM-based recommenders by maximizing the probability of positive samples and minimizing the probability of multiple negative samples at the same time. Experimental evaluations are conducted to compare DMPO with traditional recommendation methods and other LLM-based recommendation methods. The results reveal that DMPO significantly enhances the recommendation capabilities of LLMs across three real-world public datasets in few-shot scenarios. Furthermore, the experiments also demonstrate that DMPO exhibits superior generalization ability in cross-domain recommendation. A case study elucidates the reasons behind these consistent improvements and also underscores DMPO's potential as an explainable recommendation system. Our code and data are available at https://github.com/BZX667/DMPO.

With the development of location-acquisition technologies, there are a huge number of mobile trajectories generated in a variety of domains. However, due to the constraints of device and environment, many trajectories are recorded at a low sampling rate, which increases the uncertainty between two consecutive sampled points in the trajectories. Our task is to recover a high-sampled trajectory based on the irregular low-sampled trajectory. There are two major problems with traditional solutions. First, many of these methods rely on heuristic search algorithms or simple probabilistic models, which cannot well capture complex sequential dependencies or global correlations. Second, most of the previous studies adopt a common preprocessing to map the trajectory into discrete units, which bring noises. To address the above difficulties, we propose a novel Deep Hybrid Trajectory Recovery model. Our model extends the classic sequence-to-sequence generation framework by implementing a subsequence-to-sequence recovery model tailored for the current task, named subseq2seq. In order to effectively capture spatiotemporal correlations, we adopt both spatial and temporal attentions for enhancing the model performance. Furthermore, we integrate the subseq2seq with a Kalman filter component to calibrate coarse-grained discrete units as fine-grained coordinates. Extensive results on real-world datasets have shown the superiority of the proposed model.