Online Task-Free Continual Generative and Discriminative Learning via Dynamic Cluster Memory

Online Task-Free Continual Learning (OTFCL) aims to learn novel concepts from streaming data without accessing task information. Most memory-based approaches used in OTFCL are not suitable for unsupervised learning because they require accessing supervised signals to implement their sample selection mechanisms. In this study we address this issue by proposing a novel memory management approach namely the Dynamic Cluster Memory (DCM) which builds new memory clusters to capture distribution shifts over time without accessing any supervised signals. DCM introduces a novel memory expansion mechanism based on the knowledge discrepancy criterion which evaluates the novelty of the incoming data as the signal for the memory expansion ensuring a compact memory capacity. We also propose a new sample selection approach that automatically stores incoming data samples with similar semantic information in the same memory cluster while also facilitating the knowledge diversity among memory clusters. Furthermore a novel memory pruning approach is proposed to automatically remove overlapping memory clusters through a graph relation evaluation ensuring a fixed memory capacity while maintaining the diversity among the samples stored in the memory. The proposed DCM is model-free plug-and-play and can be used in both supervised and unsupervised learning without modifications. Empirical results on OTFCL experiments show that the proposed DCM outperforms the state-of-the-art while requiring fewer data samples to be stored. The source code is available at https://github.com/dtuzi123/DCM.