SimplexLoRA: Dynamic Rank Updating via Alternating Minimization with Simplex Projection

Shalygin Igor, Grigorii Davydenko, Andrey Veprikov, Aleksey Antonov, Nikolay Bushkov, Stanislav Moiseev, Aleksandr Beznosikov


Abstract
The success of large language models in real-world applications relies on parameter-efficient fine-tuning methods such as Low-Rank Adaptation (LoRA), which inserts compact, trainable adapters into selected layers. In this paper, we propose SimplexLoRA, a LoRA variant that adaptively adjusts adapter ranks during fine-tuning based on their learned importance. Unlike standard LoRA, which employs a fixed rank across all layers, SimplexLoRA optimizes per-adapter importance weights on the n-scaled simplex during a short warm-up and then freezes them, dynamically allocating capacity where it is most beneficial without increasing the overall parameter budget or inference cost. We evaluate SimplexLoRA across 12 language understanding, summarization, and reasoning tasks using DeBERTaV3, BART-large, Llama 3.1 8B, and Qwen3-8B. Our results show that SimplexLoRA consistently matches or outperforms standard LoRA and recent adaptive baselines, with the largest gains at low ranks. Our code is available at https://github.com/brain-lab-research/SimplexLoRA.
Anthology ID:
2026.findings-emnlp.2409
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
51747–51756
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.2409/
DOI:
10.18653/2026.findings-emnlp.2409
Bibkey:
Cite (ACL):
Shalygin Igor, Grigorii Davydenko, Andrey Veprikov, Aleksey Antonov, Nikolay Bushkov, Stanislav Moiseev, and Aleksandr Beznosikov. 2026. SimplexLoRA: Dynamic Rank Updating via Alternating Minimization with Simplex Projection. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 51747–51756, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
SimplexLoRA: Dynamic Rank Updating via Alternating Minimization with Simplex Projection (Igor et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.2409.pdf