Influence functions serve as crucial tools for assessing sample influence in model interpretation, subset training set selection, noisy label detection, and more. By employing the first-order Taylor extension, influence functions can estimate sample influence without the need for expensive model retraining. However, applying influence functions directly to deep models presents challenges, primarily due to the non-convex nature of the loss function and the large size of model parameters. This difficulty not only makes computing the inverse of the Hessian matrix costly but also renders it non-existent in some cases. Various approaches, including matrix decomposition, have been explored to expedite and approximate the inversion of the Hessian matrix, with the aim of making influence functions applicable to deep models. In this paper, we revisit a specific, albeit naive, yet effective approximation method known as TracIn. This method substitutes the inverse of the Hessian matrix with an identity matrix. We provide deeper insights into why this simple approximation method performs well. Furthermore, we extend its applications beyond measuring model utility to include considerations of fairness and robustness. Finally, we enhance TracIn through an ensemble strategy. To validate its effectiveness, we conduct experiments on synthetic data and extensive evaluations on noisy label detection, sample selection for large language model fine-tuning, and defense against adversarial attacks.

Graph unlearning has emerged as an essential tool for safeguarding user privacy and mitigating the negative impacts of undesirable data. Meanwhile, the advent of dynamic graph neural networks (DGNNs) marks a significant advancement due to their superior capability in learning from dynamic graphs, which encapsulate spatial-temporal variations in diverse real-world applications (e.g., traffic forecasting). With the increasing prevalence of DGNNs, it becomes imperative to investigate the implementation of dynamic graph unlearning. However, current graph unlearning methodologies are designed for GNNs operating on static graphs and exhibit limitations including their serving in a pre-processing manner and impractical resource demands. Furthermore, the adaptation of these methods to DGNNs presents non-trivial challenges, owing to the distinctive nature of dynamic graphs. To this end, we propose an effective, efficient, model-agnostic, and post-processing method to implement DGNN unlearning. Specifically, we first define the unlearning requests and formulate dynamic graph unlearning in the context of continuous-time dynamic graphs. After conducting a role analysis on the unlearning data, the remaining data, and the target DGNN model, we propose a method called Gradient Transformation and a loss function to map the unlearning request to the desired parameter update. Evaluations on six real-world datasets and state-of-the-art DGNN backbones demonstrate its effectiveness (e.g., limited performance drop even obvious improvement) and efficiency (e.g., at most 7.23$\times$ speed-up) outperformance, and potential advantages in handling future unlearning requests (e.g., at most 32.59$\times$ speed-up).