Complementary Lattice Correction for Post-Training Quantization

Tung Nguyen, Quang Hung Tran, Linh Ngo Van, Dinh Thai Hoang, Diep Nguyen, Trung Le, Duc Anh Nguyen


Abstract
Weight-only post-training quantization (PTQ) for large language models (LLMs) typically ends with the projection of floating-point weights onto a uniform integer lattice, introducing structured output error due to non-zero activation means. Existing bias correction methods compensate for this shift by adding bias terms, which is incompatible with modern bias-less architectures such as LLaMA and Mistral and only addresses the error indirectly. We propose **Complementary Lattice Correction (CLC)**, a lightweight post-quantization method that corrects projection error directly on the integer lattice without modifying the model architecture. CLC performs a budget-constrained greedy descent that selectively flips quantized weights to adjacent lattice levels. We further show that CLC provably reduces the first-moment error and admits a worst-case bound on the layer-wise mean-squared error change, which certifies non-increase under a verifiable budget condition. Experiments across multiple models, quantizers, and bit widths show that CLC consistently improves perplexity and downstream accuracy with negligible overhead.
Anthology ID:
2026.findings-emnlp.158
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:
3309–3334
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.158/
DOI:
Bibkey:
Cite (ACL):
Tung Nguyen, Quang Hung Tran, Linh Ngo Van, Dinh Thai Hoang, Diep Nguyen, Trung Le, and Duc Anh Nguyen. 2026. Complementary Lattice Correction for Post-Training Quantization. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 3309–3334, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Complementary Lattice Correction for Post-Training Quantization (Nguyen et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.158.pdf