Extended-SVD Low-Rank Adaptation: PLORA for Parameter-Efficient Fine-Tuning

Ratan Kumar Gulipilli


Abstract
We introduce Extended-SVD Low-Rank Adaptation, a parameter-efficient framework that extends the pretrained singular subspace while retaining a frozen spectral coordinate system and fixed singular-value-derived scaling. Its stabilized variant, PLORA (Procrustes Low-Rank Adaptation), applies localized Procrustes-inspired reorientation to the extended basis and confines task-specific learning to compact routing matrices P, R, and Q.

Across GLUE and vision benchmarks, PLORA achieves competitive performance with substantially fewer trainable parameters. In the full-network comparison, PLORA-r8 uses substantially fewer trainable parameters, although the performance gap varies by task. Beyond accuracy, PLORA produces task- and architecture-dependent changes in conditioning, effective rank, and subspace evolution.

Ablations show that Random Bases produce poorer routing-core conditioning and markedly lower top-r right-subspace overlap in the evaluated NLP tasks. In the evaluated settings, pretrained spectral bases are associated with more favorable optimization geometry, while Procrustes reorientation acts as an optimization-geometric regularizer. Overall, Extended-SVD provides a structured low-rank adaptation framework for studying the role of pretrained geometry in PEFT.
Anthology ID:
2026.findings-aacl.5
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
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Publisher:
Association for Computational Linguistics
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Pages:
74–93
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URL:
https://aclanthology.org/2026.findings-aacl.5/
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Cite (ACL):
Ratan Kumar Gulipilli. 2026. Extended-SVD Low-Rank Adaptation: PLORA for Parameter-Efficient Fine-Tuning. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 74–93, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Extended-SVD Low-Rank Adaptation: PLORA for Parameter-Efficient Fine-Tuning (Gulipilli, Findings 2026)
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https://aclanthology.org/2026.findings-aacl.5.pdf