REVIEW 4 major objections 4 minor 46 references
Simultaneous Relevance and Diversity: A New Recommendation Inference Approach
T0 review · 4 major / 4 minor · reviewed 2026-08-27 · deepseek-v4-flash
Pith's one-line read A recommender that learns from both liked and skipped items can raise relevance and diversity in one model, dissolving the standard exploitation-exploration trade-off.
desk verdict An elegant negative-channel extension of CF with impressive but mechanism-unconfirmed gains; needs an ablation that uses impressions without the n2p structure. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The machinery is feedback-differentiating encoding (FEEDE), built on the observation matrix $O$ and the positive-feedback matrix $X$: the negative-feedback matrix $Y=O-X$ marks observed non-engagement as explicit negative feedback. HI then runs collaborative filtering on two similarity channels: p2p uses $X^T X$ (items co-liked by the same users), and n2p uses $Y^T X$ (items disliked versus items liked by the same users), each smoothed by rank-$k$ matrix factorization. The two channels can be mixed during candidate generation with a p2p:n2p ratio, embedded as separate sub-networks in a deep neural ranking model with an interaction matrix $W$, or concatenated as $H=[X^T X;\,Y^T X]$ for realtime recommendation. The mechanism carrying the argument is that n2p similarity does not concentrate around previously liked topics, because a negative leaves many possible positives open, so diversity is a by-product of the relevance inference itself.
What would settle it
Run a head-to-head test on a dataset with full impression logs: HI versus a conventional CF that also receives $O$ (by treating observed non-engagement as training negatives) plus an explicit diversity re-ranking stage. If the latter matches or beats HI on held-out AUC/mAP and list diversity, or if HI's edge disappears when impressions are only sampled randomly, the central claim that n2p makes diversity inherent rather than a separate objective is falsified.
Extended reading notes
Core claim
The central claim is that relevance and diversity can be two inherent outcomes of a single relevance inference process, which the paper calls divergent relevance (DR). Conventional CF is characterized as positive-to-positive (p2p) inference: item similarity is derived from users who liked both items, and this converges toward a narrowing topic. HI adds negative-to-positive (n2p) inference: the fact that a user disliked an item carries signal about which other items the same user may like. By encoding negative feedback as $Y=O-X$ (observed engagement minus positive engagement) and forming cross-similarity matrices such as $Y^T X$, the model spreads predicted relevance across items the user has not yet engaged with. The paper argues that n2p's many-possible-positives-per-negative structure is what makes diversity intrinsic, and reports experiments where HI outperforms p2p-only CF and re-ranking baselines on both relevance metrics and diversity.
Load-bearing premise
The method assumes the recommender knows which items each user actually saw (the observation matrix $O$), so that a skipped item can be tagged as a true negative; if impression logs are unavailable, the negative-to-positive channel cannot be formed.
Editorial extensions
If this is right
- A single HI model can replace the common two-stage pipeline of relevance ranking plus diversity re-ranking, reducing recommendation latency while improving both metrics.
- HI's benefit grows for new users: in the batch test, the AUC advantage over baselines is larger for day-1-to-7 users than for all users, suggesting negative feedback helps cold start.
- Because n2p spreads relevance across less-similar items, recommendation lists cover more of the item space, showing up as higher recall at fixed precision and higher diversity without a relevance penalty.
- HI can be deployed at different sophistication levels, from standalone matrix factorization for realtime recommendation to embedding modules inside a deep neural network for ranking, without changing the underlying inference logic.
Reading between the lines
- If impression logs are not already recorded, a practical entry path is to approximate $O$ from UI signals such as feed position, scroll depth, or dwell time; the fidelity of that approximation is a testable limit of the method's reach.
- The p2p:n2p mixture ratio (67:33 in the paper) is a knob the paper does not fully explore; tuning it per user or per item category could produce smooth control over the convergence-versus-spread behavior.
- The divergent-relevance mechanism may also weaken the echo-chamber feedback loop over long horizons, because n2p keeps feeding varied items; the paper's experiments are short-term, so this remains an open extension.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Heterogeneous Inference (HI), an extension of collaborative filtering that combines positive-to-positive (p2p) inference with a new negative-to-positive (n2p) inference channel, enabled by a feedback-differentiating encoding (FEEDE) in which negative feedback is encoded as Y = O - X. The authors claim that n2p inference makes diversity an inherent outcome of relevance inference ('divergent relevance'), allowing relevance and diversity to improve simultaneously rather than trade off. The method is instantiated in three forms—realtime MF (HI-RT), neural ranking (HI-NN), and candidate generation—and evaluated on MovieLens and a downsampled production dataset against CF baselines with and without diversity re-ranking.
Significance. If the central claim were established, the paper would make a valuable conceptual contribution: diversity emerging from the inference process itself, rather than from a separate re-ranking stage, is a practically appealing direction for recommender systems, and the reported production A/B lift (32.05% on long-watch) is noteworthy. The timestamp-disjoint train/test splits and the use of an external CF-based similarity matrix for the diversity metric are also strengths. However, the paper's current evidence does not isolate the proposed n2p mechanism from the mere availability of extra impression information O, and the theoretical analysis is largely definitional. The significance of the paper therefore rests on whether the authors can supply controlled experiments and stronger argumentation.
major comments (4)
- [Experiments; Eq. (6)] The experimental comparison is confounded: every HI variant (HI-RT, HI-NN) is trained on both X and Y = O - X, while every baseline (CF-RT, CF-MF, CF-NN, CF-DA, CF-DM) is trained only on X. Analysis 1 explicitly establishes that FEEDE carries additional information, I(x~; O|X) > 0. Consequently, the observed gains in AUC, mAP, and diversity in Tables 1-3 could be caused simply by the extra impression matrix O rather than by the n2p inference structure. A controlled baseline that uses O in a conventional way (e.g., a CF model trained on X and Y as separate positive/negative label sets, or a model that receives O as auxiliary input) is needed to attribute the improvement to the n2p mechanism.
- [Analysis 1; Proof 1] The claimed information-theoretic proof is definitional rather than substantive. The statement I(x~; O|X) > 0 when x~ and O are not independent given X is a restatement of the definition of conditional mutual information; it does not show that FEEDE yields better engagement prediction, nor does it explain why n2p inference produces 'divergent relevance.' The proof therefore does not support the central claim that diversity is an inherent outcome of the relevance inference process. The authors should either derive a testable property of n2p inference (e.g., a condition under which the recommended-item distribution is flatter) or rely on experiments specifically designed to test that property.
- [Results and observations; Tables 1-3] The experimental results are reported as single point estimates with no variance, no number of repeated runs, and no significance tests. The text states that HI has a 'significant advantage' over baselines, but with one split for MovieLens and one downsampled production set, this claim is unsupported. The paper should provide confidence intervals or significance tests, and should describe how many random seeds or data samples were used. This is especially important because the differences in diversity metrics in Table 3 (e.g., 0.226 vs. 0.266) may be small relative to user-level variability.
- [Feedback-Differentiating Encoding (FEEDE)] The method requires that the impression matrix O is observable, as the paper acknowledges: 'FEEDE relies on an assumption that the impression of an item on a user is observable, i.e., O is known.' Many implicit feedback datasets do not record impressions, so Y = O - X cannot be formed and the n2p channel is undefined. The paper should state this applicability limitation prominently and discuss which real-world systems actually log impressions, since the general framing of the introduction suggests broader applicability than the method can deliver.
minor comments (4)
- [Abstract; Introduction] There are several typos and grammatical slips, including 'necessities' (should be 'necessitates') in the abstract and 'simultanuously' in the Results section; a careful proofreading pass is needed.
- [Evaluation metrics; Eq. (5)] The diversity metric uses the CF similarity matrix from Eq. (5), which is a reasonable choice for comparability, but the paper should clarify that this is an external similarity measure and discuss whether the conclusions are sensitive to the choice of similarity matrix.
- [Algorithms and tests] Several hyperparameters are stated without sensitivity analysis: the p2p:n2p ratio (67:33), the re-ranking weight phi in CF-DA, the loss weights alpha, gamma, lambda, and beta in Eq. (10). A brief sensitivity study or a statement that results are stable across reasonable choices would strengthen the empirical claims.
- [Figure 3] The paper references Figure 3 for user-level diversity distributions, but the figure as provided appears to be a placeholder. The authors should ensure the final version includes the actual charts with labeled axes and legends.
Circularity Check
No significant circularity: the paper's empirical claims are not forced by its definitions or by self-citation; the main weakness is an experimental confound, not a circular derivation.
full rationale
The paper's derivation chain is self-contained rather than circular. HI is defined as an extension of CF with an additional n2p channel built on Y = O - X, but that is a modeling choice, not a restatement of the relevance/diversity outcomes. Diversity is not optimized by the HI objective (Eq. 10); it is measured externally using the conventional CF similarity matrix *X defined in Eq. 5, so the reported diversity gains are not equal by construction to the model's own scoring rule. Both Test-RT and Test-BT use timestamp-disjoint training/test splits, so the AUC, precision/recall, and production long-watch results are genuine predictions on future or held-out engagement rather than refits. The only formal result, Analysis 1, shows that FEEDE carries more conditioning information than CONFE via I(x~; O|X) > 0; this is a definitional consequence of Y = O - X and is not used as the proof of the observed empirical gains. A real weakness is experimental: no baseline consumes O without the n2p structure, so the contribution of the n2p mechanism versus the extra impression information O is not isolated. That is a confound/attribution problem, not a circular derivation. The sole overlapping-author citation (Hastie et al. 2015, on ALS) is a standard related-work reference and is not load-bearing.
Assumptions & free parameters
free parameters (5)
- rank k =
10
- loss weights alpha, gamma, lambda =
not reported
- p2p:n2p mixing ratio =
67:33
- beta =
not reported
- feedback threshold =
not reported
assumptions (4)
- domain assumption O is observable, meaning impressions are known.
- domain assumption Negative feedback implies positive correlation with other items.
- domain assumption I(x~; O|X) is greater than 0.
- standard math Low-rank matrix factorization approximates item-item similarity matrices.
Cite this review
Pith. "Pith review of Simultaneous Relevance and Diversity: A New Recommendation Inference Approach." pith.science (2026). https://pith.science/paper/47MYP7OZ
@misc{pith2026200912969,
author = {Pith},
title = {Pith review of: Simultaneous Relevance and Diversity: A New Recommendation Inference Approach},
year = {2026},
howpublished = {\url{https://pith.science/paper/47MYP7OZ}},
note = {Machine review of arXiv:2009.12969}
}
read the original abstract
Relevance and diversity are both important to the success of recommender systems, as they help users to discover from a large pool of items a compact set of candidates that are not only interesting but exploratory as well. The challenge is that relevance and diversity usually act as two competing objectives in conventional recommender systems, which necessities the classic trade-off between exploitation and exploration. Traditionally, higher diversity often means sacrifice on relevance and vice versa. We propose a new approach, heterogeneous inference, which extends the general collaborative filtering (CF) by introducing a new way of CF inference, negative-to-positive. Heterogeneous inference achieves divergent relevance, where relevance and diversity support each other as two collaborating objectives in one recommendation model, and where recommendation diversity is an inherent outcome of the relevance inference process. Benefiting from its succinctness and flexibility, our approach is applicable to a wide range of recommendation scenarios/use-cases at various sophistication levels. Our analysis and experiments on public datasets and real-world production data show that our approach outperforms existing methods on relevance and diversity simultaneously.
Figures
Reference graph
Works this paper leans on
-
[1]
, " * write output.state after.block = add.period write newline
ENTRY address author booktitle chapter doi edition editor eid howpublished institution isbn issn journal key month note number organization pages publisher school series title type url volume year label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION init.state.consts #0 'before.all := #1...
-
[2]
write newline
" write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max substring 't := if while FUNCTION word.in bbl.in capitalize " " * FUNCT...
-
[3]
Adomavicius, G.; and Kwon, Y. 2011. Maximizing Aggregate Recommendation Diversity: A Graph-Theoretic Approach. In DiveRS
work page 2011
-
[4]
Adomavicius, G.; and Kwon, Y. 2012. Improving Aggregate Recommendation Diversity Using Ranking-Based Techniques. In IEEE Transactions on Knowledge and Data Engineering, 896--911
work page 2012
-
[5]
Antikacioglu, A.; and Ravi, R. 2017. Post processing recommender systems for diversity. In Proceedings of the 23rd ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, 707--716
work page 2017
-
[6]
Bradley, K.; and Smyth, B. 2001. Improving recommendation diversity. In Proceedings of the Twelfth Irish Conference on Artificial Intelligence and Cognitive Science, Maynooth, Ireland, 85--94. Citeseer
work page 2001
-
[7]
Castagnos, S.; Brun, A.; and Boyer, A. 2013. When Diversity Is Needed... But Not Expected!
work page 2013
-
[8]
Cheng, H.-T.; Koc, L.; Harmsen, J.; Shaked, T.; Chandra, T.; Aradhye, H.; Anderson, G.; Corrado, G.; Chai, W.; Ispir, M.; et al. 2016. Wide & deep learning for recommender systems. In ACM Recsys, 7--10
work page 2016
Show all 46 references
-
[9]
Covington, P.; Adams, J.; and Sargin, E. 2016. Deep Neural Networks for YouTube Recommendations. In ACM conference on recommender systems, 191--198
2016
-
[10]
V.; Gargi, U.; Gupta, S.; He, Y.; Lambert, M.; Livingston, B.; and Sampath, D
Davidson, J.; Liebald, B.; Liu, J.; Nandy, P.; Vleet, T. V.; Gargi, U.; Gupta, S.; He, Y.; Lambert, M.; Livingston, B.; and Sampath, D. 2010. The YouTube Video Recommendation System. In ACM Recsys
2010
-
[11]
V.; Dieleman, S.; and Schrauwen, B
den Oord, A. V.; Dieleman, S.; and Schrauwen, B. 2013. Deep content-based music recommendation. In NIPS, 2643--2651
2013
-
[12]
Gauci, J.; Conti, E.; Liang, Y.; Virochsiri, K.; He, Y.; Kaden, Z.; Narayanan, V.; Ye, X.; Chen, Z.; and Fujimoto, S. 2018. Horizon: Facebook's open source applied reinforcement learning platform. arXiv preprint arXiv:1811.00260
2018 arXiv
-
[13]
Ge, Y.; Zhao, S.; Zhou, H.; Pei, C.; Sun, F.; Ou, W.; and Zhang, Y. 2020. Understanding Echo Chambers in E-commerce Recommender Systems. In Proceedings of the 43rd International ACM SIGIR Conference on Research and Development in Information Retrieval, 2261--2270
2020
-
[14]
A.; and Hunt, N
Gomez-Uribe, C. A.; and Hunt, N. 2016. The netflix recommender system: Algorithms, business value, and innovation. In TMIS
2016
-
[15]
Hastie, T.; Mazumder, R.; Lee, J.; and Zadeh, R. 2015. Matrix Completion and Low-Rank SVD via Fast Alternating Least Squares. In JLMR
2015
-
[16]
He, X.; Pan, J.; Jin, O.; Xu, T.; Liu, B.; Xu, T.; Shi, Y.; Atallah, A.; Herbrich, R.; Bowers, S.; and et al. 2014. Practical lessons from predicting clicks on ads at facebook. In International Workshop on Data Mining for Online Advertising, 1--9
2014
-
[17]
Hurley, N.; and Zhang, M. 2011. Novelty and Diversity in Top-N Recommendation -- Analysis and Evaluation. In ACM Transactions on Internet Technology (TOIT), 14
2011
-
[18]
Jiang, R.; Chiappa, S.; Lattimore, T.; Gy \"o rgy, A.; and Kohli, P. 2019. Degenerate feedback loops in recommender systems. In Proceedings of the 2019 AAAI/ACM Conference on AI, Ethics, and Society, 383--390
2019
-
[19]
P.; Sivakumar, S.; and Wilkinson, D
Knijnenburg, B. P.; Sivakumar, S.; and Wilkinson, D. 2016. Recommender systems for self-actualization. In Proceedings of the 10th ACM Conference on Recommender Systems, 11--14
2016
-
[20]
Koren, Y. 2008. Factorization meets the neighborhood: a multifaceted collaborative filtering model. In ACM SIGKDD international conference on knowledge discovery and data mining, 426--434
2008
-
[21]
Koren, Y.; Bell, R.; and Volinsky, C. 2009. Matrix Factorization Techniques for Recommender Systems. In Computer, 30--37
2009
-
[22]
Krichene, W.; Mayoraz, N.; Rendle, S.; Zhang, L.; Yi, X.; Hong, L.; Chi, E.; and Anderson, J. 2018. Effcient training on very large corpora via gramian estimation. In arXiv
2018
-
[23]
D.; and Seung, H
Lee, D. D.; and Seung, H. S. 1999. Learning the parts of objects by non-negative matrix factorization. In Nature
1999
-
[24]
L'Huillier, A.; Castagnos, S.; and Boyer, A. 2014. Understanding usages by modeling diversity over time
2014
-
[25]
Mnih, A.; and Salakhutdinov, R. R. 2008. Probabilistic matrix factorization. In NIPS, 1257--1264
2008
-
[26]
T.; Hui, P.-M.; Harper, F
Nguyen, T. T.; Hui, P.-M.; Harper, F. M.; Terveen, L.; and Konstan, J. A. 2014. Exploring the filter bubble: the effect of using recommender systems on content diversity. In Proceedings of the 23rd international conference on World wide web, 677--686
2014
-
[27]
D.; Rosati, J.; Tomeo, P.; and Sciascio, E
Noia, T. D.; Rosati, J.; Tomeo, P.; and Sciascio, E. D. 2017. Adaptive multi-attribute diversity for recommender systems. volume 382-383, 234 -- 253
2017
-
[28]
Okura, S.; Tagami, Y.; Ono, S.; and Tajima, A. 2017. Embedding-based News Recommendation for Millions of Users. In SIGKDD
2017
-
[29]
Paudel, B.; F.Christoffel; and C.Newell, A. 2016. Updatable, Accurate, Diverse, and Scalable Recommendations for Interactive Applications. In ACM Transactions on Interactive Intelligent Systems
2016
-
[30]
Paudel, B.; Haas, T.; and Bernstein, A. 2017. Fewer Flops at the Top: Accuracy, Diversity, and Regularization in Two-Class Collaborative Filtering. In RecSys, 215--223
2017
-
[31]
Rendle, S. 2010. Factorization Machines. In ICDM: IEEE International Conference on Data Mining, 995--1000
2010
-
[32]
Rendle, S.; Freudenthaler, C.; and Schmidt-Thieme, L. 2010. Factorizing personalized markov chains for next-basket recommendation. In WWW: the 19th international conference on world wide web, 811--820
2010
-
[33]
Rendle, S.; and Schmidt-Thieme, L. 2010. Pairwise interaction tensor factorization for personalized tag recommendation. In WSDM: the third ACM international conference on web search and data mining, 81--90
2010
-
[34]
Salakhutdinov, R.; and Mnih, A. 2008. Bayesian probabilistic matrix factorization using Markov chain Monte Carlo. In ACM ICML, 880--887
2008
-
[35]
Salakhutdinov, R.; Mnih, A.; and Hinton, G. 2007. Restricted Boltzmann machines for collaborative filtering. In ICML, 791--798
2007
-
[36]
Srebro, N.; Rennie, J.; and Jaakkola, T. S. 2012. Maximum-margin matrix factorization. In NIPS, 1329--1336
2012
-
[37]
Steck, H. 2018. Calibrated recommendations. In Proceedings of the 12th ACM conference on recommender systems, 154--162
2018
-
[38]
Vargas, S.; Baltrunas, L.; Karatzoglou, A.; and Castells, P. 2014. Coverage, redundancy and size-awareness in genre diversity for recommender systems. In Proceedings of the 8th ACM Conference on Recommender systems, 209--216
2014
-
[39]
Wang, H.; Wang, N.; and Yeung, D.-Y. 2015. Collaborative deep learning for recommender systems. In SIGKDD, 1235--1244
2015
-
[40]
Xie, R.; Ling, C.; Wang, Y.; Wang, R.; Xia, F.; and Lin, L. 2020. Deep Feedback Network for Recommendation. In Proceedings of IJCAI-PRICAI
2020
-
[41]
L.; and Darrell, T
Zhai, A.; Kislyuk, D.; Jing, Y.; Feng, M.; Tzeng, E.; Donahue, J.; Du, Y. L.; and Darrell, T. 2017. Visual discovery at pinterest. In International Conference on World Wide Web Companion, 515--524
2017
-
[42]
Zhang, S.; Yao, L.; Sun, A.; and Tay, Y. 2019. Deep learning based recommender system: A survey and new perspectives. ACM Computing Surveys (CSUR) 52(1): 1--38
2019
-
[43]
Zhang, Z.; Zheng, X.; and Zeng, D. 2016. A framework for diversifying recommendation lists by user interest expansion. In Knowledge-Based Systems
2016
-
[44]
Zhao, X.; Zhang, L.; Ding, Z.; Xia, L.; Tang, J.; and Yin, D. 2018. Recommendations with Negative Feedback via Pairwise Deep Reinforcement Learning. In ACM SIGKDD, 1040–--1048
2018
-
[45]
Zhao, Z.; Cheng, Z.; Hong, L.; and Chi, E. H. 2015. Improving user topic interest profiles by behavior factorization. In International Conference on World Wide Web, 1406--1416
2015
-
[46]
Zou, L.; Xia, L.; Ding, Z.; Song, J.; Liu, W.; and Yin, D. 2019. Reinforcement Learning to Optimize Long-term User Engagement in Recommender Systems. In Proceedings of the 25th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining, 2810--2818
2019
Reviewed August 27, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.