Learning Structured Representations with Hyperbolic Embeddings

Most real-world datasets consist of a natural hierarchy between classes or an inherent label structure that is either already available or can be constructed cheaply. However, most existing representation learning methods ignore this hierarchy, treating labels as permutation invariant. Recent work [Zeng et al., 2022] proposes using this structured information explicitly, but the use of Euclidean distance may distort the underlying semantic context [Chen et al., 2013]. In this work, motivated by the advantage of hyperbolic spaces in modeling hierarchical relationships, we propose a novel approach HypStructure: a Hyperbolic Structured regularization approach to accurately embed the label hierarchy into the learned representations. HypStructure is a simple-yet-effective regularizer that consists of a hyperbolic tree-based representation loss along with a centering loss, and can be combined with any standard task loss to learn hierarchy-informed features. Extensive experiments on several large-scale vision benchmarks demonstrate the efficacy of HypStructure in reducing distortion and boosting generalization performance especially under low dimensional scenarios. For a better understanding of structured representation, we perform eigenvalue analysis that links the representation geometry to improved Out-of-Distribution (OOD) detection performance seen empirically. The code is available at \url{https://github.com/uiuctml/HypStructure}.

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Peer review

Reviewer 3c645/10 · confidence 3/52024-07-10

Summary

The paper introduces a novel regularization method, HypStructure, which utilizes hyperbolic geometry to improve the embedding of hierarchical relationships within feature representations. This approach enhances the learning of structured representations, reducing distortion and boosting generalization in low-dimensional scenarios. It also demonstrates superior performance in Out-of-Distribution (OOD) detection across various datasets through extensive empirical evaluation. Additionally, the paper includes an eigenvalue analysis that provides deeper insights into the structured representations, correlating positively with improved OOD detection performance. This advancement extends structured representation learning to hyperbolic spaces, achieving more discriminative and interpretable features that effectively capture the inherent hierarchies in complex datasets.

Strengths

1. The paper is the first to formally characterize properties of hierarchy-informed features via an eigenvalue analysis, and also relate it to the OOD detection task. 2. The paper is easy to read and follow, making complex concepts accessible. The use of clear definitions, structured methodology sections, and detailed discussions helps in understanding both the theoretical underpinnings and practical implications of HypStructure. Visual aids and empirical results are presented in a manner that clearly supports the claims made. 3. The significance of this work lies in its potential impact on a range of applications that require understanding and leveraging hierarchical relationships in data, such as image recognition and OOD detection.

Weaknesses

1. The main concern of this paper is the novelty. I believe the method proposed by the author in this work has been explored in many previous works. For instance, in "Hyperbolic Image Embeddings," "Hyperbolic Contrastive Learning for Visual Representations beyond Objects", etc. Although the paper characterizes properties of hierarchy-informed features via an eigenvalue analysis, the contribution is not significant enough to be accepted. 2. The writing is also not good enough for me. For instance, two examples starting from line 107 are not necessarily included in the formal paper; it is better to be placed in the supplementarity materials. There are also some repetitive expressions, for instance, in line 351 and line 353 (While the current work). 3. In summary, I believe the technical contribution of this paper is not significant enough to be accepted.

Questions

See weaknesses.

Rating

5

Confidence

3

Soundness

3

Presentation

3

Contribution

2

Limitations

As I said in the previous section, the main concern is the novelty. Potential improvements include extending the application scenarios of hyperbolic structured representations on more vision or language tasks that have not been explored before. Further theoretical investigation into establishing the error bounds of CPCC-style structured regularization objectives is of interest as well. The writing needs to be improved as well.

Reviewer gWWe5/10 · confidence 4/52024-07-11

Summary

The paper presents a novel approach, HypStructure, for learning structured representations. Comparing with the existing method, the proposed method adds an regularizer calculated from hyperbolic geometry. This approach aims to reduce distortion and improve generalization performance, particularly in low-dimensional scenarios. Extensive experiments are conducted on both the classification task and the out-of-distribution detection task.

Strengths

The paper is well organized. The paper extends and studies the existing L2-CPCC to the hyperbolic space, which effectively reduces distortion and enhances the representation of hierarchical relationships in the data. The paper also conducted comprehensive experiments as well as detailed theoretical analysis of the eigenspectrum of structured representations.

Weaknesses

If my understanding of the proposed loss term is correct, $L_flat$ is not calculated in the hyperbolic geometry. Have you tried the $L_flat$ with hyperbolic network or hyperbolic geometry. I hope the authors could provide more explanation of the combined loss in different geometries. In Section 2.1, it mentions that $D_i$ is the subset of data points with a specific class label, and $d(D_i, D_j)$ is the distance between the feature vectors of $D_i$ and $D_j$. However, it is not mentioned how the vectors for $D_i$ and $D_j$ are calculated. Is it simply the average of all the feature vectors in the subset? For Example 1 in Section 2.2, tree $T$ and nodes $G, C, D, E$ are referenced in a way that implies there should be a figure accompanied by the example. While Figure 1 is referenced shortly before this, it is meant to be accompanied by Example 2. Is there a figure that has been omitted here? Also, I would recommend proofreading the paper to correct all grammatical errors. For example, in the paragraph of Section 2.1, the first sentence “Using a composite objective as defined in Equation (2), we can enforce the distance relationship between a pair of representations in the feature space, to behave similarly as the tree metric between the same vertices” should be corrected to “Using a composite objective as defined in Equation (2), we can enforce the distance relationship between a pair of representations in the feature space to behave similarly to the tree metric between the same vertices.” This version removes the unnecessary comma and corrects “behave similarly as…” to “behave similarly to…”.

Questions

see my comments in the Weaknesses section.

Rating

5

Confidence

4

Soundness

2

Presentation

3

Contribution

3

Limitations

There are two limitations mentioned in this paper. The first being that the L2-CPCC can only approximate the structured information since it is impossible to “embed a tree $T$ into $L2$ without distortion,” and as this work extends the L2-CPCC, it would similarly have this limitation. However, this is never explicitly stated in Section 7, where it mentions that HypStructure is only limited to Euclidean classification losses. There could have been more said about the limitations, but it does suffice.

Reviewer kf6R6/10 · confidence 3/52024-07-12

Summary

This work introduces a regularization scheme based on Cophenetic Correlation Coefficient to more appropriately embed semantic label hierarchical structure in the representation. The method exploits the hierarchical benefits of hyperbolic space reformulating the CPCC regularization term to operate on the Poincare ball. The proposed method sees improvement in empirical performance demonstrating the effectiveness of the approach to learn a more separable embedding space for classification.

Strengths

⁃ The authors present the work clearly with effective use of visual and writing structure. All figures/diagrams are useful in supporting the narrative and findings. ⁃ The method is simple, highly generalizable, and leads to improved performance on benchmark tasks. It can therefore, be seen as an advantageous tool in hyperbolic learning that could possibly lead to impact and adaptation by practitioners in the field. ⁃ The theoretical and analysis are generally good, with eigenspectrum analysis supporting your claims of hierarchical structure for the most part. This is a useful analysis that provides confidence in the findings supported by appropriate proofs. ⁃ Extensive details to support replication are provided.

Weaknesses

⁃ From the visualizations presented of the embedding space, notably the UMAP, your embeddings seem to have collapsed to the boundary in many places limiting the inherent hierarchy of the embeddings, this results in a limited hierarchy being represented. This in turn, leads me to question the extent of hierarchies learnt, when discussing the core intention of the work, and the claims made. One would expect that greater performance could be achieved if this had been addressed. I am aware that boundary collapse is still an unsolved problem, but careful tuning can limit its effects. ⁃ The approach is simple but arguably not significantly novel given it is a hyperbolic reformulation of CPCC with minimal changes. With that being said, these simple methods do work somewhat well in practice and are useful to progressing the field. ⁃ The use of a Euclidean linear evaluation is a confusing direction. You are aiming to learn a hyperbolic embedding space that preserves hierarchy, yet for downstream tasks you employ a Euclidean classifier, why? You will lose the desirable properties you are aiming to capture. ⁃ Further experimentation on different hyperbolic models and downstream tasks would have helped demonstrate the generalization of the regularization to all of hyperbolic learning. Although, this cannot be expected in the rebuttal, it would have helped support the findings to present the work a more generalized approach.

Questions

See weaknesses.

Rating

6

Confidence

3

Soundness

3

Presentation

3

Contribution

3

Limitations

Broader impact statement and societal impact are seemingly missing from this work. These limitations including those limitations of the analysis should be highlighted in more detail, you mention the Euclidean loss as a limitation. If I have missed them however in the text, please correct me.

Reviewer dBDc5/10 · confidence 4/52024-07-12

Summary

The paper introduces HypStructure, a novel approach for learning structured representations using hyperbolic embeddings, which are well-suited for modeling hierarchical relationships due to their tree-like structure. The method incorporates a hyperbolic tree-based representation loss and a centering loss to embed label hierarchies into feature spaces with minimal distortion. Experiments demonstrate HypStructure's effectiveness in improving classification accuracy, especially in low-dimensional scenarios, and enhancing Out-of-Distribution (OOD) detection performance without compromising in-distribution accuracy.

Strengths

1. Although it is already theoretically proved in the related work of [70, 72] that it is not possible to embed a tree in Euclidean space without loss, it is still informative to see that In section 2.2, example 1 and example 2 give good counter-examples to show this property. 2. The paper is well-written and easy to follow, and the proposed model is simple yet effective. 3. The paper provides a formal eigenvalue analysis that links the geometry of the learned representations to their performance

Weaknesses

1. Sections 2.1, 2.2, and 3.1 are all from existing literature, which limited the contribution of the paper. Although the operations described in Section 3.1 are common hyperbolic operations, this section still lacks proper reference to the related papers. 2. In HypCPCC, the authors proposed two alternatives of the loss, * Map Euclidean vectors to Poincaré space then average. * Averaging the Euclidean vectors then map to Poincaré space. In the 1st alternative, The use of Klein weighted average incurs extra computation, Is it worth doing so?, In the 2nd alternative is exactly the same as [r2], which also calculates the prototypes for each class in hyperbolic space and then map to Poincaré space, [r2] also deploys supervised constructive learning, but the reference is missing and comparison is not stated. 3. The statement in Theorem 5.1 is incorrect, an entry of $K$, denoted as $r^h$ should be a vector, but the theorem stated that $\lambda_0 = 1 - r^1$, which does not make sense. 3. Incorrect (but fixable) definition in line 708, the proof used $\| u \| = \| v \| = 1-\epsilon $ but in the proof the authors used the fact that $\| u \| = \| v \| = 1-\epsilon^2 $ 4. Incorrect proof in Corollary A.1, the last row of the proof does not hold, Poincaré distance cannot be the same as Euclidean distance, "growing in the same trend" does not mean "proportional to". [r2] Long, Teng, et al. "Searching for actions on the hyperbole." CVPR2020

Questions

1. What is the rationale behind choosing the Klein weighted average for the first alternative in HypCPCC, considering the extra computation it incurs? 2. Can the authors provide a comparison to [r2], which is (a special case of) their second alternative of HypCPCC?

Rating

5

Confidence

4

Soundness

3

Presentation

3

Contribution

2

Limitations

The authors did not discuss the limitations in the paper.

Reviewer kf6R2024-08-09

Response to Rebuttal

Thank you for your insightful rebuttal, and clarification on points raised during the review. I'm grateful for your empirical evaluations and clarification on the boundary collapse and agree with the points made, however, I would still argue it would be beneficial to empirically demonstrate that collapse is not occurring given your strong claims made for hierarchy. Arguably, the small improvements when applying your centring method and accuracy metrics alone cannot refute the collapse claim or argue that the hierarchies you are aiming to capture are indeed captured. If I have misunderstood, or missed any further results that counter my points please do correct me. Thanks for the additional evaluation on hyperbolic networks this is a strong addition that addresses one of the identified weaknesses. I would emphasise the importance for a revised section outlining limitations, broader impact and societal for any revised manuscript, however, since you have identified these points in the rebuttal I have confidence the authors will provide this. Given my original review is positive, and that I still have a positive outlook for this work, I have maintained my score for now, and will revisit after further discussion with other reviewers.

Authorsrebuttal2024-08-10

Response to Reviewer kf6R

Thanks for the suggestion and for the support of our work! We will include the visualizations (Fig. 14 and 15) and the new results on hyperbolic settings provided in the rebuttal in the camera ready version, along with a section outlining the limitations, and broader impact as well.

Reviewer gWWe2024-08-09

Thanks for the authors' rebuttal. Personally, I think that the new results in the rebuttal have marginal improvements, and I am not sure if such improvements are statistically important, which decides the novelty of the proposed method. Therefore, I decide to keep my rate unchanged.

Authorsrebuttal2024-08-10

Response to concern about the statistical significance of the new results (Part 1)

Thanks for taking the time to go through the rebuttal, owing to the rebuttal timeline and limited space we were only able to report results corresponding to a single seed in our initial response, however we are now sharing a more exhaustive set of results with the hyperbolic settings with more evaluation metrics used in our paper, and you can find the results below (averaged over 3 seeds). **Additionally, to address your concerns about statistical significance, we performed the t-test for experiments with vs. without HypStructure, and highlighted the higher performance number only if the p-value is smaller than 0.05.** ## Experiments with the Hyperbolic Supervised Contrastive Loss Fine accuracies, coarse accuracies, and distortion measurements with the L_hyp loss . | Method | Dataset | $\delta_{rel}$ (lower) | CPCC (higher) | Fine Accuracy (higher)| Coarse Accuracy (higher)| |---|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) | CIFAR10| 0.128 (0.007) | 0.745 (0.017) | 94.58 (0.04) | 98.96 (0.01)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|CIFAR10 |**0.017 (0.001)**| **0.989 (0.001)** | **95.04 (0.02)** | **99.36 (0.02)**| | | | | | | | L_hyp (HypSupCon) |CIFAR100|0.168 (0.002)|0.664 (0.012)|75.81 (0.06)|85.26 (0.07)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|CIFAR100|**0.112 (0.005)**|**0.773 (0.008)**|**76.22 (0.14)**|**85.83 (0.06)**| | | | | | | | L_hyp (HypSupCon) |ImageNet100|0.157 (0.004)|0.473 (0.004)|89.87 (0.01)|90.41 (0.01)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|ImageNet100|**0.126 (0.002)** |**0.714 (0.003)**|**90.26 (0.01)**|**90.95 (0.01)**| Comparative Evaluation of OOD detection performance on a suite of OOD datasets with different ID datasets. OOD Detection AUROC Results on CIFAR10 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |89.45 (0.18)|93.39 (0.24)|90.18 (0.09)|98.18 (0.19) |91.31 (0.31)|92.502| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**91.11 (0.21)**|**94.45 (0.13)**|**93.52 (0.33)**|**99.05 (0.17)**|**95.24 (0.42)**|**94.674**| OOD Detection AUROC Results on CIFAR100 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |80.16 (0.08)|79.61 (0.26)|74.02 (0.45)|70.22 (0.18)|**82.35 (0.19)**|77.272| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**82.28 (0.19)**|**83.51 (0.29)**|**77.95 (0.31)**|**86.64 (0.54)**|69.86 (0.87)|**80.048**| OOD Detection AUROC Results on ImageNet100 (ID) | Method | SUN | Places365| Textures | iNaturalist |Mean| |---|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |91.96 (0.18)|90.74 (0.26)|**97.42 (0.21)** |94.04 (0.19)|93.54| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**93.87 (0.05)**|**91.56 (0.13)**|97.04 (0.16)|**95.16 (0.24)**|**94.41**| ## Experiments using the Clipped Hyperbolic Neural Network Backbone Fine accuracies, coarse accuracies, and distortion measurements with the Clipped HNN backbone | Method | Dataset | $\delta_{rel}$ (lower) | CPCC (higher) | Fine Accuracy (higher)| Coarse Accuracy (higher)| |---|:---:|:---:|:---:|:---:|:---:| | Clipped HNN | CIFAR10|0.084 (0.008)|0.604 (0.004)|94.81 (0.23)|89.71 (2.04)| | **Clipped HNN + HypStructure (Ours)**|CIFAR10 |**0.013 (0.002)**|**0.988 (0.001)**|94.97 (0.12)|**98.35 (0.22)**| | | | | | | | Clipped HNN |CIFAR100|0.098 (0.001)|0.528 (0.009)|76.46 (0.26)| 49.26 (0.73)| | **Clipped HNN + HypStructure (Ours)**|CIFAR100|**0.064 (0.006)**|**0.624 (0.005)**|**77.96 (0.14)**|**55.46 (0.61)**| | | | | | | Comparative Evaluation of OOD detection performance on a suite of OOD datasets with different ID datasets. OOD Detection AUROC Results on CIFAR10 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | Clipped HNN |92.63 (0.24)|90.74 (0.18)|88.46 (0.19)|95.66 (0.11)|92.41 (0.25)|91.98| | **Clipped HNN + HypStructure (Ours)**|**95.41 (0.44)**|**93.91 (0.32)**|**92.31 (0.41)**|**96.87 (0.21)**|**94.92 (0.31)**|**94.68**| OOD Detection AUROC Results on CIFAR100 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | Clipped HNN |89.94 (0.16)|83.77 (0.23)|77.26 (0.33)|82.87 (0.29)| 82.35 (0.15)|83.23| |**Clipped HNN + HypStructure (Ours)**|**91.56 (0.21)**|**84.31 (0.09)**|**78.45 (0.28)**|**87.53 (0.52)**|**83.44 (0.37)**|**85.06**| ... (continued in the next response)

Authorsrebuttal2024-08-10

Response to concern about the statistical significance of the new results (Part 2)

... (continued from Part 1 of this response) **Summary**: Based on the above results over multiple seeds, we can clearly observe that our proposed method leads to a **statistically significant** and consistent improvement in performance in terms of classification accuracies with a significantly more evident reduction in other metrics, including distortion of the representations, and a higher improvement on the mean AUROC in the OOD detection tasks, with improvements upto 3% across a suite of OOD datasets. >I think that the new results in the rebuttal have marginal improvements, and I am not sure if such improvements are statistically important, which decides the novelty of the proposed method We humbly disagree with the reviewers’ comment here and based on the above results, argue that the results would be a strong addition in demonstrating the wide-applicability of our proposed method **across tasks**, as has also been noted by Reviewer kf6R. Note that it has been discussed in multiple prior works [1] that improving accuracy on both classification as well as OOD detection tasks is fairly challenging. Furthermore, we would also like to point the reviewer to the global response where we clearly outline the novelty of our contribution which is not limited to the performance with hyperbolic losses/backbones, but is a lot more general, where **our work addresses the challenges of embedding explicit hierarchies and shows strong performance across tasks, learns interpretable representations and also draws important theoretical connections to tasks such as OOD detection, which are all very different from the prior works in the literature**. We hope that this clarifies the questions raised by the reviewer about the statistical significance and the novelty of the results. We would be happy to discuss any further questions about the work, and would really appreciate an increase in score if reviewers’ concerns are addressed. [1] OpenOOD: Benchmarking Generalized Out-of-Distribution Detection,Yang et. al, NeurIPS ‘22, Datasets and Benchmarks Track [2] Learning Structured Representations by Embedding Class Hierarchy, Zeng et. al, ICLR ‘23

Authorsrebuttal2024-08-13

Regarding further discussion and any additional concerns

Dear Reviewer gWWe, We express gratitude for your time spent on reviewing our work and your valuable comments, and hope that - the additional and exhaustive comparative experiments shared above help address your concerns about the statistical significance of our method's performance - the positive comments and feedback from all three other reviewers (kf6R, 3c64 and dBDc) on our theoretical contributions, overall experimentation and insights may help clarify the novelty and impact of our work to the community With the rebuttal discussion window closing today, we look forward to engaging in further discussion to confirm if your concerns have been addressed and if there are any other questions regarding our work, that we can answer.

Authorsrebuttal2024-08-10

Additional Results for the experiments with Hyperbolic Settings

We are now sharing a more exhaustive set of results with the hyperbolic settings with more evaluation metrics used in our paper, with the results below (averaged over 3 seeds). **We also perform the t-test for experiments with vs. without HypStructure, and highlighted the higher performance number only if the p-value is smaller than 0.05, for statistical significance** ## Experiments with the Hyperbolic Supervised Contrastive Loss Fine accuracies, coarse accuracies, and distortion measurements with the L_hyp loss . | Method | Dataset | $\delta_{rel}$ (lower) | CPCC (higher) | Fine Accuracy (higher)| Coarse Accuracy (higher)| |---|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) | CIFAR10| 0.128 (0.007) | 0.745 (0.017) | 94.58 (0.04) | 98.96 (0.01)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|CIFAR10 |**0.017 (0.001)**| **0.989 (0.001)** | **95.04 (0.02)** | **99.36 (0.02)**| | | | | | | | L_hyp (HypSupCon) |CIFAR100|0.168 (0.002)|0.664 (0.012)|75.81 (0.06)|85.26 (0.07)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|CIFAR100|**0.112 (0.005)**|**0.773 (0.008)**|**76.22 (0.14)**|**85.83 (0.06)**| | | | | | | | L_hyp (HypSupCon) |ImageNet100|0.157 (0.004)|0.473 (0.004)|89.87 (0.01)|90.41 (0.01)| | **L_hyp (HypSupCon) + HypStructure (Ours)**|ImageNet100|**0.126 (0.002)** |**0.714 (0.003)**|**90.26 (0.01)**|**90.95 (0.01)**| Comparative Evaluation of OOD detection performance on a suite of OOD datasets with different ID datasets. OOD Detection AUROC Results on CIFAR10 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |89.45 (0.18)|93.39 (0.24)|90.18 (0.09)|98.18 (0.19) |91.31 (0.31)|92.502| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**91.11 (0.21)**|**94.45 (0.13)**|**93.52 (0.33)**|**99.05 (0.17)**|**95.24 (0.42)**|**94.674**| OOD Detection AUROC Results on CIFAR100 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |80.16 (0.08)|79.61 (0.26)|74.02 (0.45)|70.22 (0.18)|**82.35 (0.19)**|77.272| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**82.28 (0.19)**|**83.51 (0.29)**|**77.95 (0.31)**|**86.64 (0.54)**|69.86 (0.87)|**80.048**| OOD Detection AUROC Results on ImageNet100 (ID) | Method | SUN | Places365| Textures | iNaturalist |Mean| |---|:---:|:---:|:---:|:---:|:---:| | L_hyp (HypSupCon) |91.96 (0.18)|90.74 (0.26)|**97.42 (0.21)** |94.04 (0.19)|93.54| | **L_hyp (HypSupCon) + HypStructure (Ours)**|**93.87 (0.05)**|**91.56 (0.13)**|97.04 (0.16)|**95.16 (0.24)**|**94.41**| ## Experiments using the Clipped Hyperbolic Neural Network Backbone Fine accuracies, coarse accuracies, and distortion measurements with the Clipped HNN backbone | Method | Dataset | $\delta_{rel}$ (lower) | CPCC (higher) | Fine Accuracy (higher)| Coarse Accuracy (higher)| |---|:---:|:---:|:---:|:---:|:---:| | Clipped HNN | CIFAR10|0.084 (0.008)|0.604 (0.004)|94.81 (0.23)|89.71 (2.04)| | **Clipped HNN + HypStructure (Ours)**|CIFAR10 |**0.013 (0.002)**|**0.988 (0.001)**|94.97 (0.12)|**98.35 (0.22)**| | | | | | | | Clipped HNN |CIFAR100|0.098 (0.001)|0.528 (0.009)|76.46 (0.26)| 49.26 (0.73)| | **Clipped HNN + HypStructure (Ours)**|CIFAR100|**0.064 (0.006)**|**0.624 (0.005)**|**77.96 (0.14)**|**55.46 (0.61)**| | | | | | | Comparative Evaluation of OOD detection performance on a suite of OOD datasets with different ID datasets. OOD Detection AUROC Results on CIFAR10 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | Clipped HNN |92.63 (0.24)|90.74 (0.18)|88.46 (0.19)|95.66 (0.11)|92.41 (0.25)|91.98| | **Clipped HNN + HypStructure (Ours)**|**95.41 (0.44)**|**93.91 (0.32)**|**92.31 (0.41)**|**96.87 (0.21)**|**94.92 (0.31)**|**94.68**| OOD Detection AUROC Results on CIFAR100 (ID) | Method | SVHN | Textures| Places365 | LSUN | iSUN | Mean | |---|:---:|:---:|:---:|:---:|:---:|:---:| | Clipped HNN |89.94 (0.16)|83.77 (0.23)|77.26 (0.33)|82.87 (0.29)| 82.35 (0.15)|83.23| |**Clipped HNN + HypStructure (Ours)**|**91.56 (0.21)**|**84.31 (0.09)**|**78.45 (0.28)**|**87.53 (0.52)**|**83.44 (0.37)**|**85.06**| **Summary**: Based on the above results over multiple seeds, we can clearly observe that our proposed method leads to a **statistically significant** and consistent improvement in performance in terms of classification accuracies with a significantly more evident reduction in other metrics, including distortion of the representations, and a higher improvement on the mean AUROC in the OOD detection tasks, with improvements upto 3% across a suite of OOD datasets.

Reviewer 3c642024-08-12

Thanks for the authors' rebuttal. The rebuttal strengthens my understanding of this paper. Combined with other reviews and rebuttals. I still believe the plug-in approach is useful, but the improvements on CIFAR 10 and 100 are not obvious. However, the theoretical understanding part and mathematical proof are valuable to the community. I would like to raise the score to 5. Good luck!

Authorsrebuttal2024-08-12

Response to Reviewer 3c64

Thanks for raising your score and for the support of our work and it's contributions! We greatly appreciate the time you spent reviewing our paper, and going through the rebuttal and the other reviews, as well as your valuable suggestions for improving our work. We hope that the improvements across datasets, tasks and settings in terms of accuracies, distortion metrics and OOD scores are clearer in our updated set of results (as shared in response to reviewer gWWe, as well as the global comment with new results), and are grateful that our rebuttal could address your concerns. We would be happy to discuss further if you have any more questions about our work.

Reviewer dBDc2024-08-13

Thank you for your detailed response and the clarifications provided. I appreciate the effort you put into addressing my concerns. After reviewing your explanation, most of my concerns have been resolved. Although I acknowledge that the novelty and technical contribution might be somewhat limited, as pointed out by Reviewer 3c64, I believe that your proofs and the extensive experiments you conducted will still provide value to the community. In light of this, I will be raising my rating.

Authorsrebuttal2024-08-13

Response to Reviewer dBDc

Dear Reviewer dBDc, Thanks for your valuable feedback in the support of our work and for raising your rating! We are happy to see that our responses could address your concerns. We will include the clarifications and corrections to the proofs based on your suggestions, in the revised manuscript, and if you have any further questions for our work, we would be happy to continue the discussion.

Program Chairsdecision2024-09-25

Decision

Accept (poster)

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