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1. Discriminative Self-Paced Group-Metric Adaptation for Online Visual Identification

   https://doi.org/10.1109/TPAMI.2022.3200036  

   Zhou, Jiahuan; Su, Bing; Wu, Ying (August 2022, IEEE Transactions on Pattern Analysis and Machine Intelligence)

   Existing solutions to instance-level visual identification usually aim to learn faithful and discriminative feature extractors from offline training data and directly use them for the unseen online testing data. However, their performance is largely limited due to the severe distribution shifting issue between training and testing samples. Therefore, we propose a novel online group-metric adaptation model to adapt the offline learned identification models for the online data by learning a series of metrics for all sharing-subsets. Each sharing-subset is obtained from the proposed novel frequent sharing-subset mining module and contains a group of testing samples that share strong visual similarity relationships to each other. Furthermore, to handle potentially large-scale testing samples, we introduce self-paced learning (SPL) to gradually include samples into adaptation from easy to difficult which elaborately simulates the learning principle of humans. Unlike existing online visual identification methods, our model simultaneously takes both the sample-specific discriminant and the set-based visual similarity among testing samples into consideration. Our method is generally suitable to any off-the-shelf offline learned visual identification baselines for online performance improvement which can be verified by extensive experiments on several widely-used visual identification benchmarks. 

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2. Learning Visual Instance Retrieval from Failure: Efficient Online Local Metric Adaptation from Negative Samples

   https://doi.org/10.1109/TPAMI.2019.2918208  

   Zhou, Jiahuan; Wu, Ying (May 2019, IEEE Transactions on Pattern Analysis and Machine Intelligence)

   Existing visual instance retrieval (VIR) approaches attempt to learn a faithful global matching metric or discriminative feature embedding offline to cover enormous visual appearance variations, so as to directly use it online on various unseen probes for retrieval. However, their requirement for a huge set of positive training pairs is very demanding in practice and the performance is largely constrained for the unseen testing samples due to the severe data shifting issue. In contrast, this paper advocates a different paradigm: part of the learning can be performed online but with nominal costs, so as to achieve online metric adaptation for different query probes. By exploiting easily-available negative samples, we propose a novel solution to achieve the optimal local metric adaptation effectively and efficiently. The insight of our method is the local hard negative samples can actually provide tight constraints to fine tune the metric locally. Our local metric adaptation method is generally applicable to be used on top of any offline-learned baselines. In addition, this paper gives in-depth theoretical analyses of the proposed method to guarantee the reduction of the classification error both asymptotically and practically. Extensive experiments on various VIR tasks have confirmed our effectiveness and superiority. 

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3. Continual Learning Using a Kernel-Based Method Over Foundation Models

   Momeni, Saleh; Mazumder, Sahisnu; Liu, Bing (February 2025, The 39th Annual AAAI Conference on Artificial Intelligence)

   Continual learning (CL) learns a sequence of tasks incre- mentally. This paper studies the challenging CL setting of class-incremental learning (CIL). CIL has two key chal- lenges: catastrophic forgetting (CF) and inter-task class sep- aration (ICS). Despite numerous proposed methods, these issues remain persistent obstacles. This paper proposes a novel CIL method, called Kernel Linear Discriminant Analy- sis (KLDA), that can effectively avoid CF and ICS problems. It leverages only the powerful features learned in a foundation model (FM). However, directly using these features proves suboptimal. To address this, KLDA incorporates the Radial Basis Function (RBF) kernel and its Random Fourier Fea- tures (RFF) to enhance the feature representations from the FM, leading to improved performance. When a new task ar- rives, KLDA computes only the mean for each class in the task and updates a shared covariance matrix for all learned classes based on the kernelized features. Classification is performed using Linear Discriminant Analysis. Our empir- ical evaluation using text and image classification datasets demonstrates that KLDA significantly outperforms baselines. Remarkably, without relying on replay data, KLDA achieves accuracy comparable to joint training of all classes, which is considered the upper bound for CIL performance. The KLDA code is available at https://github.com/salehmomeni/klda. 

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4. Online Dynamics Learning for Predictive Control with an Application to Aerial Robots

   Jiahao, Tom Z.; Chee, Kong Yao; Hsieh, M. Ani (May 2023, Proceedings of The 6th Conference on Robot Learning)

   Liu, Karen; Kulic, Dana; Ichnowski, Jeff (Ed.)

   In this work, we consider the task of improving the accuracy of dynamic models for model predictive control (MPC) in an online setting. Although prediction models can be learned and applied to model-based controllers, these models are often learned offline. In this offline setting, training data is first collected and a prediction model is learned through an elaborated training procedure. However, since the model is learned offline, it does not adapt to disturbances or model errors observed during deployment. To improve the adaptiveness of the model and the controller, we propose an online dynamics learning framework that continually improves the accuracy of the dynamic model during deployment. We adopt knowledge-based neural ordinary differential equations (KNODE) as the dynamic models, and use techniques inspired by transfer learning to continually improve the model accuracy. We demonstrate the efficacy of our framework with a quadrotor, and verify the framework in both simulations and physical experiments. Results show that our approach can account for disturbances that are possibly time-varying, while maintaining good trajectory tracking performance. 

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5. Online Dynamics Learning for Predictive Control with an Application to Aerial Robots

   Jiahao, Tom Z.; Chee, Kong Yao; Hsieh, M. Ani (May 2023, Proceedings of The 6th Conference on Robot Learning, PMLR)

   Liu, Karen; Kulic, Dana; Ichnowski, Jeff (Ed.)

   In this work, we consider the task of improving the accuracy of dynamic models for model predictive control (MPC) in an online setting. Although prediction models can be learned and applied to model-based controllers, these models are often learned offline. In this offline setting, training data is first collected and a prediction model is learned through an elaborated training procedure. However, since the model is learned offline, it does not adapt to disturbances or model errors observed during deployment. To improve the adaptiveness of the model and the controller, we propose an online dynamics learning framework that continually improves the accuracy of the dynamic model during deployment. We adopt knowledge-based neural ordinary differential equations (KNODE) as the dynamic models, and use techniques inspired by transfer learning to continually improve the model accuracy. We demonstrate the efficacy of our framework with a quadrotor, and verify the framework in both simulations and physical experiments. Results show that our approach can account for disturbances that are possibly time-varying, while maintaining good trajectory tracking performance. 

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