2026
Federated fine-tuning when clients use different LoRA ranks
In federated fine-tuning, phones and servers often train LoRA adapters of different sizes. The usual fix pads the smaller ones with zeros, which wastes bandwidth. NSVD-Agg merges adapters with a nested SVD instead, so no padding is sent.
- 53.1% less communication, with lower final loss, across 7 seeds on Llama-3.2-3B and Qwen2.5-3B (Wilcoxon p = 0.0156; Cohen's d = 5.76–7.89).
- A stationarity bound under non-convex assumptions, with a four-term error decomposition that isolates rank-induced projection error.
Paper: Beyond Zero-Padding: Nested-SVD Aggregation for Heterogeneous-Rank Federated LoRA