arXiv Machine Learning By Simone Ricci, Niccol\`o Biondi, Federico Pernici, Alberto Del Bimbo

Hyperspherical Simplex Representations for Backward-Compatible Retrieval

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The paper introduces hyperspherical simplex representations derived from softmax outputs and logits to enable backward-compatible retrieval across independently trained models. By exploiting the simplex geometry induced by cross‑entropy training, the authors propose a deterministic linear transformation that realigns class prototypes when new classes are added, eliminating the need for compatibility‑specific training or architectural changes. Theoretical analysis under von Mises–Fisher assumptions shows that these aligned regular‑simplex representations satisfy the formal backward‑compatibility conditions, and empirical results demonstrate competitive performance on standard benchmarks without extra losses or mappings.

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arXiv Machine Learning
Jun 2

When Hard Negatives Hurt: Bridging the Generative-Discriminative Gap in Hard Negative Synthesis for Retrieval

arXiv:2606. 01304v1 Announce Type: new Abstract: Hard negative mining has become the dominant strategy for training retrievers, yet it faces intrinsic limitations: negatives are bounded by corpus availability, selected by retriever score rather than diagnostic value, and increasingly contaminated by false positives as the retriever improves.

By Zhicheng Zhang, Jiwei Tang, Kuicai Dong, Xiaopeng Li, Jieming Zhu, Jingyu Li, Qianhui Zhu, Fengyuan Lu, Wang Jiaheng, Gang Wang, Hai-Tao Zheng, Zhaocheng Du