Return of Frustratingly Easy Domain Adaptation
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Abstract (arXiv)
Unlike human learning, machine learning often fails to handle changes between training (source) and test (target) input distributions. Such domain shifts, common in practical scenarios, severely damage the performance of conventional machine learning methods. Supervised domain adaptation methods have been proposed for the case when the target data have labels, including some that perform very well despite being "frustratingly easy" to implement. However, in practice, the target domain is often unlabeled, requiring unsupervised adaptation. We propose a simple, effective, and efficient method for unsupervised domain adaptation called CORrelation ALignment (CORAL). CORAL minimizes domain shift by aligning the second-order statistics of source and target distributions, without requiring any target labels. Even though it is extraordinarily simple--it can be implemented in four lines of Matlab code--CORAL performs remarkably well in extensive evaluations on standard benchmark datasets.
Key facts. Cited by 391 papers in the map (data through 14 Oct 2026). First posted on arXiv 17 Nov 2015.
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Citing papers per year: 2021: 105; 2022: 90; 2023: 62; 2024: 56; 2025: 48; 2026: 30.
391 papers.
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- 2021Generalizing to Unseen Domains: A Survey on Domain Generalizationcited by 766
- 2021Towards Personalized Federated Learningcited by 464
- 2021Towards Out-Of-Distribution Generalization: A Surveycited by 436
- 2021Domain Adaptation for Medical Image Analysis: A Surveycited by 352
- 2022Scaling & Shifting Your Features: A New Baseline for Efficient Model Tuningcited by 294
- 2021Fishr: Invariant Gradient Variances for Out-of-Distribution Generalizationcited by 186
- 2022MIC: Masked Image Consistency for Context-Enhanced Domain Adaptationcited by 178
- 2021Exploiting the Intrinsic Neighborhood Structure for Source-free Domain Adaptationcited by 177
- 2021Generalized Source-free Domain Adaptationcited by 175
- 2021Delving into Deep Imbalanced Regressioncited by 158
- 2022Diverse Weight Averaging for Out-of-Distribution Generalizationcited by 148
- 2021The Norm Must Go On: Dynamic Unsupervised Domain Adaptation by Normalizationcited by 131
38 more
- 2021CDTrans: Cross-domain Transformer for Unsupervised Domain Adaptationcited by 129
- 2022Deep Unsupervised Domain Adaptation: A Review of Recent Advances and Perspectivescited by 98
- 2022Model Ratatouille: Recycling Diverse Models for Out-of-Distribution Generalizationcited by 97
- 2022Attracting and Dispersing: A Simple Approach for Source-free Domain Adaptationcited by 94
- 2021Unsupervised Domain Adaptation of Object Detectors: A Surveycited by 93
- 2023UniverSeg: Universal Medical Image Segmentationcited by 91
- 2021Invariant Information Bottleneck for Domain Generalizationcited by 86
- 2021Extending the WILDS Benchmark for Unsupervised Adaptationcited by 86
- 2021Unsupervised Multi-source Domain Adaptation Without Access to Source Datacited by 76
- 2021Cross-domain Contrastive Learning for Unsupervised Domain Adaptationcited by 76
- 2022Agree to Disagree: Diversity through Disagreement for Better Transferabilitycited by 70
- 2021VDM-DA: Virtual Domain Modeling for Source Data-free Domain Adaptationcited by 69
- 2023PromptStyler: Prompt-driven Style Generation for Source-free Domain Generalizationcited by 59
- 2021HSVA: Hierarchical Semantic-Visual Adaptation for Zero-Shot Learningcited by 57
- 2022Unsupervised Domain Adaptation for Nighttime Aerial Trackingcited by 56
- 2021MetaAlign: Coordinating Domain Alignment and Classification for Unsupervised Domain Adaptationcited by 54
- 2021AdaptSum: Towards Low-Resource Domain Adaptation for Abstractive Summarizationcited by 51
- 2021DINE: Domain Adaptation from Single and Multiple Black-box Predictorscited by 51
- 2021Style Normalization and Restitution for Domain Generalization and Adaptationcited by 46
- 2021Online Adaptation to Label Distribution Shiftcited by 44
- 2021Tune it the Right Way: Unsupervised Validation of Domain Adaptation via Soft Neighborhood Densitycited by 44
- 2023Prompt-based Distribution Alignment for Unsupervised Domain Adaptationcited by 44
- 2022A Survey on Heterogeneous Federated Learningcited by 42
- 2021Feature Stylization and Domain-aware Contrastive Learning for Domain Generalizationcited by 40
- 2022SSDA3D: Semi-supervised Domain Adaptation for 3D Object Detection from Point Cloudcited by 37
- 2023Subspace Identification for Multi-Source Domain Adaptationcited by 37
- 2021One-Class Classification: A Surveycited by 35
- 2021Domain Generalization via Inference-time Label-Preserving Target Projectionscited by 35
- 2021ToAlign: Task-oriented Alignment for Unsupervised Domain Adaptationcited by 33
- 2021A Survey of Unsupervised Domain Adaptation for Visual Recognitioncited by 31
- 2022High-Modality Multimodal Transformer: Quantifying Modality & Interaction Heterogeneity for High-Modality Representation Learningcited by 31
- 2021Transformer-Based Source-Free Domain Adaptationcited by 30
- 2021Iterative Feature Matching: Toward Provable Domain Generalization with Logarithmic Environmentscited by 30
- 2023RLSbench: Domain Adaptation Under Relaxed Label Shiftcited by 30
- 2021Self-supervised Autoregressive Domain Adaptation for Time Series Datacited by 29
- 2022Domain Generalization using Pretrained Models without Fine-tuningcited by 29
- 2021Unsupervised Domain Adaptation with Variational Approximation for Cardiac Segmentationcited by 28
- 2021Generation, augmentation, and alignment: A pseudo-source domain based method for source-free domain adaptationcited by 28
50 most cited of 391 All 391 (JSON)
- 2026Rethinking Projector Training in Multimodal LLMs13 Oct 2026
- 2026One-Slide Calibration of Pathology Foundation Models6 Oct 2026
- 2026FLOW: Feature-Level Optimal Warping for Generalized Remote Physiological Measurement30 Sep 2026
- 2026Evo2Team: When Do Evolved Skills Transfer? From Selection to Deployment28 Sep 2026
- 2026Measurement-Gated Provenance Attenuation for Frozen EEG Representations26 Sep 2026
- 2026Transfer Learning for Evolving Domains11 Sep 2026
- 2026Few-Shot Video Recognition via Hierarchical Metric Learning4 Sep 2026
- 2026MASH-Bench: Diagnosing Cross-Source Failure in Mass-Shooting Risk Classification23 Aug 2026
- 2026SPARC: Subspace Position-Aware Robust Few-Shot Calibration for Distribution-Shifted Industrial Anomaly Detection19 Aug 2026
- 2026Measuring and Detecting Harmful AI Sycophancy6 Aug 2026
- 2026Mitigating Domain Shift in Conditioned Floor Plan Generation: Synthetic Pre-training for Data-Efficient Adaptation7 Jul 2026
- 2026Automated Background Swapping for Robustness against Spurious Backgrounds30 Jun 2026
38 more
- 2026GCT-MARL: Graph-Based Contrastive Transfer for Sample-Efficient Cooperative Multi-Agent Reinforcement Learning23 Jun 2026
- 2026ASALT: Adaptive State Alignment for Lateral Transfer in Multi-agent Reinforcement Learning23 Jun 2026
- 2026FreqKD: Frequency-Decoupled Cross-Modal Knowledge Distillation for Infrared Object Detection10 Jun 2026
- 2026Diagnosing and Mitigating Domain Shift in Permission-Based Android Malware Detection9 May 2026
- 2026A Robust Unsupervised Domain Adaptation Framework for Medical Image Classification Using RKHS-MMD5 May 2026
- 2026Stabilizing In-Context Multi-Source Domain Adaptation for Biomedical Images Through Controls22 Apr 2026
- 2026MIRANDA: MId-feature RANk-adversarial Domain Adaptation toward climate change-robust ecological forecasting with deep learning1 Apr 2026
- 2026Boundary-aware Prototype-driven Adversarial Alignment for Cross-Corpus EEG Emotion Recognition18 Mar 2026
- 2026Sample-Efficient Adaptation of Drug-Response Models to Patient Tumors under Strong Biological Domain Shift17 Mar 2026
- 2026Stabilizing Test-Time Adaptation of High-Dimensional Simulation Surrogates via D-Optimal Statistics17 Feb 2026
- 2026TRACE: Trajectory Recovery for Continuous Mechanism Evolution in Causal Representation Learning29 Jan 2026
- 2026GTFMN: Guided Texture and Feature Modulation Network for Low-Light Image Enhancement and Super-Resolution27 Jan 2026
- 2026Source-Free Domain Adaptation by Optimizing Batch-Wise Cosine Similarity24 Jan 2026
- 2026Region-aware Spatiotemporal Modeling with Collaborative Domain Generalization for Cross-Subject EEG Emotion Recognition22 Jan 2026
- 2026Cross-Domain Object Detection Using Unsupervised Image Translation16 Jan 2026
- 2026SfMamba: Efficient Source-Free Domain Adaptation via Selective Scan Modeling13 Jan 2026
- 2026Backpropagation-Free Test-Time Adaptation for Lightweight EEG-Based Brain-Computer Interfaces12 Jan 2026
- 2026OSCAR: Open-Set CAD Retrieval from a Language Prompt and a Single Image12 Jan 2026
- 2025Advanced Unsupervised Learning: A Comprehensive Overview of Multi-View Clustering Techniques4 Dec 2025
- 2025Mapping of Lesion Images to Somatic Mutations1 Dec 2025
- 2025Passive Dementia Screening via Facial Temporal Micro-Dynamics Analysis of In-the-Wild Talking-Head Video17 Nov 2025
- 2025Boomda: Balanced Multi-objective Optimization for Multimodal Domain Adaptation11 Nov 2025
- 2025Machine and Deep Learning for Indoor UWB Jammer Localization3 Nov 2025
- 2025Active transfer learning for structural health monitoring31 Oct 2025
- 2025Geometric Moment Alignment for Domain Adaptation via Siegel Embeddings16 Oct 2025
- 2025Ivan-ISTD: Rethinking Cross-domain Heteroscedastic Noise Perturbations in Infrared Small Target Detection14 Oct 2025
- 2025Consistent Assistant Domains Transformer for Source-free Domain Adaptation2 Oct 2025
- 2025Online Adaptation via Dual-Stage Alignment and Self-Supervision for Fast-Calibration Brain-Computer Interfaces23 Sep 2025
- 2025FedFusion: Federated Learning with Diversity- and Cluster-Aware Encoders for Robust Adaptation under Label Scarcity23 Sep 2025
- 2025Cross-Modal Retrieval with Cauchy-Schwarz Divergence15 Sep 2025
- 2025ACE and Diverse Generalization via Selective Disagreement9 Sep 2025
- 2025Learning Domain- and Class-Disentangled Prototypes for Domain-Generalized EEG Emotion Recognition1 Sep 2025
- 2025Uncertainty Awareness on Unsupervised Domain Adaptation for Time Series Data26 Aug 2025
- 2025Cross-Cancer Knowledge Transfer in WSI-based Prognosis Prediction19 Aug 2025
- 2025CORE-ReID V2: Advancing the Domain Adaptation for Object Re-Identification with Optimized Training and Ensemble Fusion6 Aug 2025
- 2025Active Learning and Transfer Learning for Anomaly Detection in Time-Series Data5 Aug 2025
- 2025Partial Domain Adaptation via Importance Sampling-based Shift Correction27 Jul 2025
- 2025Handling Out-of-Distribution Data: A Survey25 Jul 2025
50 newest of 391 All 391 (JSON)
- 2024Source-Free Domain Adaptation with Diffusion-Guided Source Data Generationcited by 4
- 2025Unsupervised Detection of Distribution Shift in Inverse Problems using Diffusion Modelscited by 4
- 2023Transcending Domains through Text-to-Image Diffusion: A Source-Free Approach to Domain Adaptationcited by 0
- 2024Adversarial Domain Adaptation for Cross-user Activity Recognition Using Diffusion-based Noise-centred Learningcited by 0
- 2025Unsupervised Detection of Distribution Shift in Inverse Problems using Diffusion Models16 May 2025
- 2024Adversarial Domain Adaptation for Cross-user Activity Recognition Using Diffusion-based Noise-centred Learning6 Aug 2024
- 2024Source-Free Domain Adaptation with Diffusion-Guided Source Data Generation7 Feb 2024
- 2023Transcending Domains through Text-to-Image Diffusion: A Source-Free Approach to Domain Adaptation2 Oct 2023
- 2021Generalizing to Unseen Domains: A Survey on Domain Generalizationcited by 766
- 2021Towards Personalized Federated Learningcited by 464
- 2021Towards Out-Of-Distribution Generalization: A Surveycited by 436
- 2021Domain Adaptation for Medical Image Analysis: A Surveycited by 352
- 2022Scaling & Shifting Your Features: A New Baseline for Efficient Model Tuningcited by 294
- 2021Fishr: Invariant Gradient Variances for Out-of-Distribution Generalizationcited by 186
- 2022MIC: Masked Image Consistency for Context-Enhanced Domain Adaptationcited by 178
- 2021Exploiting the Intrinsic Neighborhood Structure for Source-free Domain Adaptationcited by 177
- 2021Generalized Source-free Domain Adaptationcited by 175
- 2021Delving into Deep Imbalanced Regressioncited by 158
- 2022Diverse Weight Averaging for Out-of-Distribution Generalizationcited by 148
- 2021The Norm Must Go On: Dynamic Unsupervised Domain Adaptation by Normalizationcited by 131
12 most cited of 377 All 377 (JSON)
- 2026One-Slide Calibration of Pathology Foundation Models6 Oct 2026
- 2026FLOW: Feature-Level Optimal Warping for Generalized Remote Physiological Measurement30 Sep 2026
- 2026Evo2Team: When Do Evolved Skills Transfer? From Selection to Deployment28 Sep 2026
- 2026Measurement-Gated Provenance Attenuation for Frozen EEG Representations26 Sep 2026
- 2026Transfer Learning for Evolving Domains11 Sep 2026
- 2026Few-Shot Video Recognition via Hierarchical Metric Learning4 Sep 2026
- 2026MASH-Bench: Diagnosing Cross-Source Failure in Mass-Shooting Risk Classification23 Aug 2026
- 2026SPARC: Subspace Position-Aware Robust Few-Shot Calibration for Distribution-Shifted Industrial Anomaly Detection19 Aug 2026
- 2026Measuring and Detecting Harmful AI Sycophancy6 Aug 2026
- 2026Mitigating Domain Shift in Conditioned Floor Plan Generation: Synthetic Pre-training for Data-Efficient Adaptation7 Jul 2026
- 2026Automated Background Swapping for Robustness against Spurious Backgrounds30 Jun 2026
- 2026GCT-MARL: Graph-Based Contrastive Transfer for Sample-Efficient Cooperative Multi-Agent Reinforcement Learning23 Jun 2026
12 newest of 377 All 377 (JSON)